LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


ELECTRO-MAGNETIC 
ORE   SEPARATION 


BY 
C.    GODFREY   GUNTHER 


WITH  ILLUSTRATIONS 


1909 

HILL    PUBLISHING' COMPANY 
505   PEARL  STREET,    NEW   YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 
The  Engineering  and  Mining  Journal  —  Power  —  American  Machinist 


/t'C 


COPYRIGHT,  1909,  BY  THE  HILL  PUBLISHING  COMPANY 


ENTERED  AT  STATIONERS'  HALL,  LONDON,  ENGLAND 


All  rights  reserved 


Hill  Publishing  Company,  New  York,  U.  S.  A. 


PREFACE 

THIS  book  has  been  prepared  to  gather  into  convenient  form 
the  published  information  on  the  magnetic  separation  of  ores.  The 
compilation  has  been  supplemented  by  data  from  the  writer's  obser- 
vations and  an  extensive  correspondence  with  mill  managers  and 
manufacturers.  It  has  been  attempted  to  include  only  that  which 
is  of  present  commercial  importance. 

The  writer  wishes  to  express  his  thanks  to  the  many  who  have 
aided  him  in  the  collection  of  data  for  this  work,  and  especially 
to  Messrs.  W.  R.  Ingalls,  W.  L.  'Austin,  Erminio  Ferraris,  C.  Q. 
Payne,  Adriano  Contreras,  S.  Norton,  James  Hebbard,  and  Ben- 
jamin Hodge,  and  also  to  the  Humboldt  Engineering  Works  Co., 
Elektro-Magnetische  Gesellschaft,  Marchegger  Maschinenfabrik, 
United  Iron  Works  Co.,  and  the  Dings  Electromagnetic  Sepa- 
rator Co. 

EL  PASO,  TEXAS,  September,  1908. 


in 


INTRODUCTION 

THE  magnetic  properties  of  certain  minerals  have  long  been 
recognized,  and  their  concentration  through  magnetism  can  lay 
no  claim  to  novelty.  A  patent  was  awarded  in  England  on  a 
process  for  separating  iron  minerals  by  means  of  a  magnet  in  1792, 
and  in  this  country  a  separator  having  a  conveyor  belt  for  present- 
ing ore  beneath  electro-magnets  excited  by  cells  was  employed  in 
separating  magnetite  from  apatite  in  New  York  State  in  1852. 

The  earlier  attempts  at  magnetic  separation  naturally  were 
directed  toward  the  separation  of  the  most  strongly  magnetic  sub- 
stances. The  first  separators  were  employed  in  separating  iron 
from  brass  filings  and  turnings,  metallic  iron  from  furnace  prod- 
ucts, and  magnetite,  the  most  strongly  magnetic  of  minerals,  from 
gangue.  The  next  step  in  the  process  was  in  roasting,  or  calcining, 
certain  iron  minerals  which  might  by  such  means  be  transformed 
into  strongly  magnetic  compounds  and  separated  from  their  ad- 
mixtures. The  steady  development  of  improved  apparatus  and 
more  intense  fields  has  constantly  broadened  the  field  of  magnetic 
separation  until  minerals  previously  considered  nonmagnetic  are 
separated  commercially. 

Beginning  with  the  crude  machines  which  employed  perma- 
nent magnets  to  attract  the  magnetic  particles  and  brushes  to 
detach  the  material  so  collected,  a  great  variety  of  separators  has 
been  devised  and  patented,  and  many  of  them  have  been  placed  in 
commercial  operation.  The  magnetic  separator  has  been  developed, 
in  most  instances,  for  the  exploitation  of  individual  ore  deposits, 
and  the  different  types  and  modifications  so  produced  might  well 
form  subject  matter  for  a  book.  In  the  United  States  alone  over 
three  hundred  patents  have  been  granted. 

In  view  of  the  above  facts  the  broad  practice  of  magnetic  sepa- 
ration is  incapable  of  monopoly  and  its  application  is  not  de- 
termined by  any  one  machine.  The  process  suitable  to  the  treat- 
ment of  the  ore  under  consideration  having  been  carefully  chosen, 


VI  INTRODUCTION 

it  will  be  found  that  any  one  of  several  machines  will  perform 
the  functions  of  the  actual  separation. 

In  its  own  field,  which  will  be  hereinafter  outlined,  magnetic 
separation  is  a  useful  adjunct  to  the  specific-gravity  processes, 
but  it  is  in  no  sense  a  competitor  with  these  processes  except  in 
the  concentration  of  magnetite  iron  ores,  and  in  this  application 
is  a  succsss  backed  up  by  many  years  of  profitable  operation. 


CONTENTS 


CHAPTER  PAGE 

INTRODUCTION v 

I.     MAGNETISM  APPLIED  TO  ORE  DRESSING 3 

II.     PRINCIPLES  OF  MAGNETIC  SEPARATION  AND  PREPARATION  OF 

THE  ORE  FOR  TREATMENT 9 

III.  SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS       »       .       .       22 

IV.  SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS  ,       .       .       .       61 
V.     THE  CONCENTRATION  OF  MAGNETITE  ORES  .        .        .       .        .       79 

VI.    THE  SEPARATION  OF  PYRITE  AND  BLENDE    .       .       .       .       .115 

VII.    THE  SEPARATION  OF  SIDERITE  FROM  BLENDE  «,  138 

VIII.     SEPARATION  OF  MISCELLANEOUS  ORES  AND  MINERALS  153 


ELECTRO-MAGNETIC   ORE  SEPARATION 


OF   THE 

UNIVERSITY 

OF 


MAGNETISM    APPLIED    TO    ORE    DRESSING 

ALL  substances — solid,  liquid,  and  gaseous — are  either  attracted 
or  repelled  by  a  magnet,  though  in  most  cases  this  influence  is 
too  feeble  to  be  apparent  except  with  delicately  adjusted  apparatus. 
The  atmosphere  has  a  definite  magnetic  attractability  and  the 
magnetic  behavior  of  solids  may  be  said  to  be  controlled  by  the 
magnetic  qualities  of  the  surrounding  medium;  if  a  substance 
is  more  permeable  to  magnetism  than  air,  it  is  attracted;  if  less 
permeable,  it  is  repelled.  The  permeability  of  air  (air  being  the 
most  common  medium)  is  taken  as  1,  and  the  permeabilities  of 
all  other  substances  are  referred  to  it  as  unity.  The  permeabilities 
of  substances  more  strongly  attracted  than  air  are  therefore  repre- 
sented by  values  greater  than  1,  and  are  called  paramagnetics ; 
substances  less  permeable  than  air  are  represented  by  values  less 
than  1,  and  are  called  diamagnetics.  The  permeability  of  the 
diamagnetics  is  so  nearly  unity  that  the  phenomenon  of  magnetic 
repulsion  is  riot  a  familiar  one. 

The  lines  of  force  of  a  magnetic  circuit  pass  along  the  path  of 
least  resistance;  in  other  words,  they  pass  through  the  most  per- 
meable substance  available.  Paramagnetic  particles,  introduced 
into  a  magnetic  field,  tend  to  aline  themselves  in  the  direction 
of  the  lines  of  force  in  precisely  the  same  manner  that  a  compass 
needle  alines  itself  with  the  magnetic  meridian.  Paramagnetics 
concentrate  the  lines  of  force,  while  diamagnetics  cause  the  lines 
of  force  to  go  around  them.  The  passage  of  lines  of  force  through 
particles  induces  magnetic  polarity  in  them,  and  they  gather  in 
tufts  or  chains,  North  pole  to  South  pole,  and  are  all  held  by 
the  energizing  magnet.  The  force  with  which  these  particles  are 
attracted  is  a  function  of  their  permeability,  the  intensity  of  the 
field,  and  the  time  they  are  subjected  to  its  influence. 

The  paramagnetic  minerals  have  been  divided  for  convenience 

3  - 


4  ELECTRO-MAGNETIC   ORE   SEPARATION 

into  two  classes :  those  which  are  attracted  and  held  by  a  common 
permanent  magnet,  called  ferromagnetic  minerals.,  and  those  not 
so  attracted,  referred  to  as  feebly  magnetic  minerals.  The  ferro- 
magnetic minerals  are  magnetite,  pyrrhotite,  ilmenite,  chromite, 
and  franklinite  in  typical  specimens. 

Various  investigators  have  made  attempts  to  determine  the 
specific  magnetic  permeabilities  of  minerals,  but  without  uniform- 
ly reliable  results.  This  is  due  to  two  causes :  the  variable  mag- 
netic permeability  of  the  same  mineral  from  different  localities 
(and  even  of  different  specimens  from  the  same  locality)  and  the 
unreliability  of  the  available  methods  for  determining  the  per- 
meability of  minerals.  The  rod  method,  employed  in  testing  the 
permeability  of  iron,  is  not  applicable  to  minerals,  as  rods  of 
sufficient  length  of  pure  minerals  are  not  available.  The  methods 
employed  are  based  on  a  comparison  of  the  permeabilities  of 
crushed  and  sized  minerals  with  crushed  and  sized  cast  iron,  or 
filings.  The  figures  so  obtained  are  affected  by  the  size  and  shape 
of  the  particles  tested,  the  amount  tested,  whether  the  charge  is 
packed  tight  or  loose,  etc.,  which  makes  the  results  of  comparative 
value  only. 

In  view  of  the  above  facts  the  permeabilities  of  various  min- 
erals, as  determined,  do  not  form  a  reliable  guide  in  the  consid- 
eration of  ores,  and  a  preliminary  test  of  the  ore  in  question  must 
be  made  to  determine  the  applicability  of  magnetic  separation, 
unless  the  ore  be  magnetite  or  one  capable  of  transformation  into 
magnetic  oxide. 

While  chemically  pure  minerals  possess  magnetic  permeability 
independently  of  any  iron  they  may  carry,  in  practice  it  is  almost 
always  the  effect  of  a  trace  or  more  of  iron,  either  chemically 
combined  or  present  as  an  impurity,  that  is  utilized  for  separation. 
In  minerals  which  combined  iron  renders  separable  the  magnetic 
permeability  varies  more  or  less  regularly  with  the  amount  of 
iron  combined;  but  minerals  which  depend  for  their  separation 
upon  the  presence  of  iron  as  an  impurity  are  subject  to  wide  vari- 
ations in  permeability,  and  are  therefore  more  unreliable  subjects 
for  magnetic  separation. 

The  paramagnetic  metals  are  iron,  nickel,  cobalt,  manganese, 
chromium,  cerium,  titanium,  palladium,  platinum,  and  osmium. 
Oxygen  is  paramagnetic  (liquid  air  is  attracted  and  held  by  a 
magnet)  and  sulphur  is  diamagnetic;  the  oxides  are  therefore 


MAGNETISM  APPLIED  TO  ORE  DRESSING  5 

more  likely  to  be  magnetic  than  the  sulphides  of  the  same  metals, 
and  in  like  manner  the  oxides  are  usually  more  strongly  magnetic 
than  the  carbonates.  That  the  chemical  composition  of  a  sub- 
stance does  not  determine  its  magnetic  properties,  however,  is 
strikingly  shown  in  the  mineral  pyrite  (FeS,,  46.7  per  cent,  iron) 
which  is  too  feebly  magnetic  to  be  separated  by  the  most  intense 
field  yet  produced ;  and  also  in  the  bromide  of  copper,  a  compound 
of  two  diamagnetic  elements,  which  is  paramagnetic.  The  occur- 
rence of  strongly  magnetic  galena  at  Gem,  Idaho,  is  another 
striking  instance  of  the  variable  magnetic  behavior  of  minerals. 

The  crystalline  form  of  a  compound  has  an  effect  on  its  mag- 
netic properties,  as  has  also  water  of  crystallization.  The  tem- 
perature at  which  separation  takes  place  also  exercises  an  influence : 
Langguth  ("  Elektromagnetische  Aufbereitung,"  p.  5)  separated 
readily  a  zinc  blende,  warm,  which  was  with  difficulty  effected 
when  cold. 

Much  has  been  written  concerning  the  magnetic  properties  of 
various  salts  and  alloys,  in  the  investigation  of  which  peculiar 
manifestations  of  magnetism  have  been  observed.  While  throwing 
light,  perhaps,  on  the  magnetic  behavior  of  matter,  these  results 
are  hardly  of  importance  in  the  practical  subject  of  magnetic 
separation.  (For  the  theories  regarding  the  magnetic  properties 
of  matter  the  reader  is  referred  to  the  writings  of  Poisson,  Cou- 
lomb, Ampere,  Becquerel,  Weber,  Burgman,  Kohlrausch,  Plucker, 
Tyndall,  Faraday,  Delcasse,  Dolter,  Wiedman  and  others.) 

THE  FIELD  OF  MAGNETIC    SEPARATION 

The  applications  of  magnetism  to  ore  dressing  fall  naturally 
under  two  heads :  the  concentration  of  magnetic  minerals  from 
their  gangues,  and  the  separation  of  two  or  more  minerals  of 
similar  specific  gravity  in  the  products  of  a  preliminary  water 
concentration. 

Magnetic  concentration  has  been  applied  principally  to  the 
treatment  of  magnetic  iron  ores,  eliminating  the  gangue,  and  at  the 
same  time  effecting  a  partial  separation  of  phosphorus  and  sulphur 
minerals  which  are  frequent  and  objectionable  contaminations. 
The  concentration  of  these  magnetite  ores  is  the  oldest,  and 
to-day  one  of  the  most  important  applications  of  magnetism  to 
ore  dressing.  A  plant  for  the  concentration  of  siderite  from 


6  ELECTRO-MAGNETIC  ORE  SEPARATION 

gangue  has  been  in  operation  in  France  for  a  number  of  years, 
and  another  is  now  being  constructed  in  Hungary.  Magnetic  con- 
centration has  also  been  applied  to  the  treatment  of  ores  carrying 
chalcopyrite.  This  mineral  has  a  tendency  to  slime,  when  crushed, 
which  gives  rise  to  an  important  loss  in  subsequent  wet  concentra- 
tion; but  after  roasting  it  is  readily  saved  by  magnetic  attrac- 
tion, even  if  in  a  fine  state  of  division.  There  are  other  minor 
applications  of  magnetic  concentration  such  as  leucite  from  lava, 
manganese  ores,  garnetiferous  schists,  etc. 

In  magnetic  separation,  as  distinct  from  concentration,  the  ap- 
plications are  more  numerous  and  complex.  There  occur  in  nature 
many  combinations  of  minerals  whose  specific  gravities  are  too  sim- 
ilar to  permit  of  their  separation  by  any  of  the  usual  concentrating 
devices.  In  such  combinations  where  one  of  the  minerals  is  mag- 
netic, or  may  be  rendered  magnetic  by  the  application  of  heat, 
magnetism  offers  an  efficient,  and  often  the  only,  method  of 
separation. 

For  reasons  connected  with  the  subsequent  reduction  of  zinc 
ores  the  presence  of  iron  is  highly  objectionable,  and  ores  which 
carry  more  than  a  small  percentage  of  iron  are  severely  penalized. 
This,  together  with  the  similarity  of  the  specific  gravities  of  the 
iron  and  zinc  minerals  often  found  together,  gives  rise  to  one  of 
the  most  important  applications  of  magnetic  separation.  Zinc 
blende  frequently  occurs  with  pyrite,  marcasite  or  siderite,  all 
minerals  of  specific  gravities  too  similar  to  permit  a  separation 
by  specific-gravity  methods.  Pyrite  and  marcasite  are  not  capable 
of  separation  in  their  raw  state,  but  become  magnetic  on  roasting; 
siderite  is  separable  by  magnetic  fields  of  high  intensity,  and  may 
also  be  transformed  into  a  strongly  magnetic  compound  by  calcina- 
tion. Oxidized  zinc  minerals  also  occur  in  important  ore  bodies 
with  limonite,  and  here  again  the  difference  in  the  specific  grav- 
ities of  the  minerals  is  too  slight  to  permit  a  separation  by  milling 
methods.  Limonite  is  slightly  magnetic  and  may  be  removed  in 
its  raw  state  by  fields  of  high  intensity,  and  may  also  be  calcined 
to  the  strongly  magnetic  oxide  of  iron  and  removed  as  such.  Zinc 
blende  carrying  sufficient  combined  iron  to  be  magnetic  occurs  in 
many  localities  in  Colorado  and  elsewhere  in  conjunction  with 
pyrite,  from  which  it  may  be  separated  by  magnetism  without 
preliminary  treatment. 

At  Broken  Hill,  N".  S.  W.,  immense  ore  bodies  carry  blende  to- 


MAGNETISM  APPLIED  TO  ORE  DRESSING  7 

gether  with  rhodonite  and  garnet,  minerals  of  similar  specific 
gravity.  The  middling  products  from  water  concentration  of  ores; 
carrying  these  minerals  are  separated  by  magnetism.  The  peculiar 
ore  bodies  at  Franklin  Furnace,  N.  J.,  are  treated  exclusively  by 
magnetic  separation. 

Magnetic  separation  has  found  application  in  the  treatment  of 
monazite  sands,  in  the  separation  of  tin-tungsten  concentrate,  for 
the  removal  of  magnetic  contaminations  from  corundum,  in  heavy 
sulphide  concentrates,  in  the  separation  of  chalcopyrite-blende-sid- 
erite  concentrates,  and  in  other  cases. 

The  principal  applications  of  magnetism  to  ore  dressing  as 
represented  by  successful  installations  have  been  stated  above,  but 
there  are  many  other  separations  which  are  entirely  practicable 
but  not  at  present  in  commercial  use.  The  low  prices  and  high 
standards  of  iron  ores  obtaining  in  the  United  States  do  not  per- 
mit of  the  exploitation  of  ore  fields  which  in  another  country 
would  be  of  great  value.  As  our  purer  ores  are  exhausted,  and 
prices  rise,  there  will  be  a  steady  increase  in  application  of  mag- 
netism to  the  concentration  of  iron  ores,  not  alone  in  the  treatment 
of  natural  magnetite,  but  also  for  the  lean  hematites  and  limonites 
which  cannot  now  be  worked  at  a  profit. 

MAGNETIC  SEPARATION  AS  A  PROCESS 

Where  applicable,  this  process  possesses  all  the  advantages  held, 
by  other  separation  processes,  and,  in  addition,  is  independent  of 
gravity.  A  prerequisite  of  success  in  any  separation  process  is  the 
existence  of  the  minerals  to  be  separated  as  free  particles,  and  in 
this  magnetic  separation  constitutes  no  exception.  Furthermore, 
all  separating  devices  work  better  on  sized  material  than  on  a 
mixture  of  coarse  and  fine  particles.  While  sizing  is  necessary 
in  many  specific-gravity  methods,  it  is  desirable,  but  not  impera- 
tive, in  magnetic  separation.  The  preparation  of  the  ore  for 
treatment  by  crushing  and  sizing  represents,  in  any  case,  a  large 
proportion  of  the  total  cost  of  the  process,  whether  the  final  sepa- 
ration be  made  by  jigs  and  tables  or  by  magnetic  separators. 

The  magnetic  separator  has  been  developed  into  an  efficient 
machine  which  is  economical  of  power,  both  for  operation  and 
excitation  of  the  magnets,  not  liable  to  break  down  or  get  out  of 
adjustment,  is  easily  operated  by  anyone  with  the  intelligence  neces- 


8  ELECTRO-MAGNETIC  ORE   SEPARATION 

sary  to  operate  any  of  the  usual  concentrating  machines,  and  is 
not  a  source  of  large  expense  bills  for  repairs  and  renewals. 

To  sum  the  matter  up,  the  only  difference  between  specific- 
gravity  and  magnetic-separation  processes  is  that  one  utilizes  dif- 
ferences in  the  specific  gravities  of  the  minerals  to  be  separated, 
and  the  other  utilizes  the  differences  in  their  magnetic  permea- 
bilities. Where,  however,  the  ore  must  be  roasted  or  dried  before 
separation,  this  item  must  be  charged  against  the  magnetic  treat- 
ment of  which  it  is  a  prerequisite. 


II 

PRINCIPLES  OF  MAGNETIC  SEPARATION  AND  PREPA- 
RATION OF  THE  ORE  FOR  TREATMENT 

To  separate  successfully  a  mixture  of  magnetic  and  nonmag- 
netic particles  a  separator  must  fulfill  the  following  requirements : 
It  must  make  a  proper  presentation  to  the  magnetic  field  of  the 
mixture  to  be  separated;  it  must  bring  about  the  attraction  of  the 
magnetic  particles  by  a  uniform  field  of  suitable  intensity;  it 
must  remove  the  magnetic  particles  so  attracted  from  the  field  and 
cause  their  discharge  from  the  separator. 

PRESENTATION  or  THE  ORE  MIXTURE  TO  THE  MAGNETIC  FIELD 

A  proper  presentation  of  the  mixture  to  be  separated  to  the 
magnetic  field  is  of  primary  importance.  The  ore  must  enter  the 
field  in  such  a  manner  that  the  individual  particles  will  be  free  to 
be  attracted  according  to  their  permeabilities.  The  ore  must,  there- 
fore, be  fed  in  a  thin,  even  layer  or  sheet  in  order  that  the  mag- 
netic particles  may  not  be  hindered  in  their  attraction  toward  the 
separating  pole  by  intervening  nonmagnetic  particles.  Theoretic- 
ally, this  layer  should  be  but  one  particle  deep,  and  in  the  separa- 
tion of  very  feebly  magnetic  minerals  this  is  carried  out  in 
practice.  In  the  separation  of  magnetite,  either  natural  or  artifi- 
cial, and  the  ferromagnetic  minerals,  a  deeper  feed  is  permissible, 
and  consequently  a  greater  capacity  for  the  separator.  When  the 
feed  is  more  than  one  particle  deep  the  upward  rush  of  magnetic 
particles  toward  the  pole  is  apt  to  entrain  nonmagnetic  particles 
and  carry  them  into  the  magnetic  product.  This  loss  is  not  a  seri- 
ous one  with  fields  of  suitable  intensity;  that  is,  with  fields  just 
sufficiently  strong  to  attract  the  magnetic  particles.  In  many  sepa- 
rators provision  is  made  for  the  removal  of  entrained  particles  from 
the  magnetic  concentrate  by  a  blast  of  air  or  a  jet  of  water  while 
it  is  still  under  the  influence  of  the  field,  or  by  the  turning  over 

9 


10  ELECTRO-MAGNETIC  ORE   SEPARATION 

of  the  magnetic  concentrate  by  causing  it  to  pass  from  one  pole 
to  another  of  opposite  polarity,  which  operation  causes  the  mag- 
netic particles  to  reverse  their  individual  positions  as  they  pass 
from  one  pole  to  the  opposite  sign. 

The  above  considerations  apply  more  particularly  to  the  pres- 
entation of  the  ore  mixture  by  conveyor  belts,  shaking  plates, 
drums,  and  rolls.  When  the  ore  is  presented  to  the  magnets  as 
a  thin  sheet  falling  past  the  poles,  or  when  the  separation  is 
carried  out  under  water,  the  feed  being  introduced  in  suspension 
in  a  stream  of  water,  entrainment  is  a  less  serious  difficulty. 

It  is  also  essential  to  good  work  that  the  feed  be  constant  in 
amount  and  presented  at  a  uniform  distance  from  the  separating 
pole,  that  all  parts  of  it  may  be  acted  upon  equally  by  the  field, 
the  intensity  of  which  varies  with  the  distance  from  the  separating 
pole.  As  the  intensity  of  the  field  is  greatest,  and  the  attraction 
consequently  strongest,  at  the  poles,  decreasing  directly  with  dis- 
tance from  them,  it  follows  that  the  ore  mixture  should  be  intro- 
duced into  the  field  as  near  the  separating  pole  as  is  practicable. 

The  speed  at  which  the  ore  is  presented  to  the  magnets,  or  the 
time  the  ore  is  under  the  influence  of  the  field,  is  also  a  factor 
of  prime  importance.  A  definite  length  of  time  is  necessary  for 
the  induction  of  magnetism,  the  time  required  for  induction,  and 
consequent  attraction,  varying  inversely  with  the  permeability 
of  the  mineral  treated.  That  the  speed  of  passage  of  the  ore 
through  the  magnetic  field  must  be  regulated  according  to  the  per- 
meability of  the  mineral  separated  is  well  illustrated  by  the  fol- 
lowing experiment.1 

A  Mechernich  separator  was  fitted  with  a  thin  conveyor  belt 
passing  between  the  poles  of  the  magnets  and  so  arranged  that  its 
speed  might  be  varied  at  will.  A  mixture  of  minerals  crushed  to 
pass  a  0.75  millimeter  aperture  was  fed  upon  the  belt  and  passed 
through  the  field  at  different  speeds,  the  intensity  of  the  field  re- 
maining constant.  With  the  belt  traveling  100  meters  per  minute 
only  magnetite  was  removed  by  the  magnet ;  at  70  meters  rhodonite 
was  partially  removed,  but  ferruginous  blende  was  quite  unaffected ; 
at  50  meters  the  rhodonite  was  completely  removed  but  the  blende 
still  remained  unaffected ;  at  40  meters  per  minute  the  blende  was 
partially  removed,  and  at  30  meters  completely  removed,  the  in- 
tensity of  the  field  remaining  constant  throughout  the  test. 

1 "  Elektromagnetische  Aufbereitung,"  E.  Langguth,  p.  16. 


PRINCIPLES  OF   MAGNETIC  SEPARATION  11 

Separators  whose  feed  is  presented  to  the  magnets  as  a  thin 
sheet  falling  in  front  of  the  separating  poles  are  limited  in  their 
application  to  minerals  of  high  permeability  by  the  speed  of  the 
passage  of  the  ore  through  the  field. 

ATTRACTION  OF  THE  MAGNETIC  PARTICLES 

Magnetic  attraction  in  performing  a  separation  is  opposed  by 
some  other  force,  usually  gravity,  the  magnetic  particles  being 
lifted  from  the  mixture  under  separation,  or  prevented  from  fall- 
ing when  fed,  for  instance,  upon  a  revolving  drum  or  cylinder. 
Gravity  is  often  supplemented  by  some  other  agency,  as  centrif- 
ugal force,  a  blast  of  air  or  a  stream  of  water  acting  against  the 
magnetic  attraction.  The  opposing  forces  of  magnetic  attraction 
and  gravity,  or  centrifugal  force,  may  be  delicately  adjusted,  and 
separations  effected  between  minerals  having  but  slight  differences 
in  permeability. 

The  intensity  of  a  magnetic  field  should  be  adjusted  to  the 
permeabilities  of  the  minerals  it  is  to  be  called  upon  to  separate, 
and  the  field  should  be  uniform  throughout  its  separating  zone 
in  order  that  all  portions  of  the  ore  fed  may  be  equally  acted  upon. 
The  air  gap  between  the  poles  should  be  as  narrow  as  is  permitted 
by  the  conveying  device  and  the  ore  sheet  passing  between  them. 
The  intensity  of  the  field  is  determined  by  the  ampere-turns  of  the 
exciting  coils,  the  cross  section,  the  length  and  the  material  form- 
ing the  magnetic  circuit,  the  distance  between  the  poles  and  the 
shape  of  the  pole  pieces.  The  intensity  of  the  field  is  controlled 
in  practice  by  the  current  allowed  to  flow  through  the  exciting 
coils  and  the  distance  between  the  poles,  which  in  most  separators 
is  adjustable. 

In  magnetic  separators,  for  minerals  of  feeble  permeability 
especially,  it  is  desirable  to  produce  a  dense  field,  or  concentration 
of  the  lines  of  force  along  the  separating  zone.  This  may  be  ob- 
tained by  beveling  the  pole  pieces,  by  the  device  of  two  parallel 
magnetized  cylinders,  by  a  series  of  sharp  projections  on  the  sepa- 
rating pole  or  armature  placed  between  the  poles,  by  a  laminated 
construction  of  pole  pieces,  or  by  an  armature  made  up  of  alternate 
disks  of  magnetic  and  nonmagnetic  material.  The  reason  for 
this  concentration  is  that  the  lines  of  force,  in  their  passage  across 
the  gap  of  the  separating  field  between  the  poles,  seek  to  travel  as 


12  ELECTRO-MAGNETIC  ORE   SEPARATION 

far  as  possible  through  the  iron  of  the  pole  pieces  or  armature, 
as  offering  less  resistance  to  their  passage  than  air,  resulting  in  a 
concentration  of  these  lines  of  force  where  the  air  gap  is  shortest. 
In  separators  employing  but  one  separating  field  it  is  usual  in 
order  that  no  magnetic  particle  may  escape  attraction  to  introduce 
the  feed  at  the  strongest  part  of  the  field.  Where  more  than  one 
separating  field  is  employed  the  ore  should  be  passed  through  fields 
of  gradually  increasing  strength.  The  effect  of  this  is  to  remove 
minerals  of  different  permeabilities  as  separate  products,  the  most 
strongly  magnetic  by  the  first  and  weakest  field,  and  the  most 
feebly  magnetic  by  the  last  and  strongest  field,  and  to  prevent 
entrainment  by  avoiding  the  rush  of  strongly  magnetic  particles 
in  a  field  of  greater  intensity  than  is  necessary  for  their  attraction. 
If  separators  having  only  one  separating  field  are  employed  it  is 
usually  necessary  to  operate  two  or  more  machines  tandem,  with 
fields  of  progressively  increasing  intensity. 

REMOVAL  OF  THE  ATTRACTED  PARTICLES  FROM  THE  MAGNETS 

The  removal  of  the  attracted  particles  from  the  magnets  may 
be  accomplished  in  several  ways,  depending  upon  the  form  and 
kind  of  magnet  employed. 

With  separators  which  draw  the  magnetic  particles  against 
the  magnet  itself,  these  particles  must  be  removed  either  by  force 
or  by  interrupting  the  attraction  by  breaking  the  current  on  the 
exciting  coils.'  With  the  old  permanent-magnet  separators,  and 
with  separators  employing  revolving  magnets  which  do  not  change 
their  polarity  during  revolution,  scrapers  or  brushes  must  be  re- 
sorted to  in  order  to  effect  the  removal  of  the  attracted  particles. 
With  wet  separators  a  jet  of  water  may  be  employed.  With  electro- 
magnets the  exciting  current  may  be  automatically  interrupted 
and  the  attracted  particles  allowed  to  fall;  this  is  only  possible 
with  certain  constructions  and  has  not  been  in  general  use. 

With  separators  which  employ  secondarily  induced  magnets  to 
effect  the  separation  these  may  be  caused  to  pass  beyond  the  field 
of  the  primaries  and  the  attracted  particles  so  dropped.  A  con- 
struction which  has  found  extensive  application  employs  a  rotat- 
ing cylinder,  or  armature,  revolving  between  the  primary  poles  to 
effect  the  separation.  Here  any  point  on  the  cylinder  changes  its 
polarity  during  revolution,  and,  at  a  position  90  degrees  from  the 


PRINCIPLES  OF   MAGNETIC   SEPARATION  13 

separating  zone,  passes  from  one  sign  to  the  opposite,  where  the 
attracted  particles  are  dropped.  The  cylinder  may  retain  suffi- 
cient residual  magnetism  to  hold  strongly  magnetic  particles,  even 
at  the  neutral  point,  in  which  case  brushes  or  scrapers  may  be 
necessary  to  overcome  the  feeble  attraction  due  to  this  cause. 

In  another  construction  advantage  is  taken  of  a  property  of 
the  lines  of  force  emanating  from  a  magnet  pole  to  concentrate 
upon  points  of  magnetic  material — in  other  words,  employing 
secondarily  induced  magnetic  points  to  remove  the  particles  at- 
tracted by  the  primary  magnet.  Here  the  secondary  magnet  points 
are  caused  to  pass  out  of  the  influence  of  the  primary  magnet,  and, 
upon  losing  their  magnetism,  drop  the  attracted  particles. 

With  separators  which  act  by  deflecting  the  magnetic  particles 
from  a  falling  sheet  of  ore  adjustable  diaphragms  are  used  to 
divide  the  particles  according  to  their  degree  of  deflection  from 
the  verticle:  any  particles  which  may  have  become  attached  to 
the  magnet  poles  may  be  dropped  by  breaking  the  current  for  an 
instant. 

In  separators  which  employ  but  one  separating  zdne,  the  mag- 
net, and  means  of  removing  the  particles  attracted  by  the  same, 
should  be  so  arranged  that  at  least  three  different  products  are  ob- 
tained— a  concentrate,  a  middling  and  a  tailing.  This  may  be 
accomplished  by  gradually  decreasing  the  strength  of  the  field  at 
the  discharge  and  employing  adjustable  diaphragms  to  separate 
the  products,  the  most  weakly  magnetic  falling  first  and  the  most 
strongly  magnetic  last. 

NECESSITY  OF  MAKING  A  MIDDLING  PRODUCT 

In  the  crushed  ore  submitted  to  any  process  for  separation  or 
concentration  there  is  always  a  certain  proportion  of  composite 
particles  containing  both  the  valuable  mineral  and  waste,  and  this 
may  not  be  avoided,  even  by  excessively  fine  crushing,  which  is 
usually  undesirable  on  account  of  the  quantity  of  dust  or  slime 
produced.  These  particles  are  too  rich  to  be  allowed  to  go  into 
the  tailing,  and  too  lean  to  be  included  in  the  concentrate ;  in  any 
scheme  of  treatment,  therefore,  provision  should  be  made  for  the 
recovery  of  such  particles  as  a  middling  product.  With  magnetic 
separators  it  is  usually  advisable  to  carry  on  the  first  magnet  en- 
countered by  the  ore  the  lowest  current  which  will  separate  the 


14  ELECTRO-MAGNETIC  ORE   SEPARATION 

pure  magnetic  particles,  and  a  sufficient  current  on  the  last  magnet 
to  remove  all  the  particles  carrying  a  portion  of  the  magnetic  min- 
eral. The  result  of  this  is  a  clean  magnetic  concentrate  from  the 
first  magnet  and  a  clean  nonmagnetic  product,  with  a  middling 
product,  for  the  retreatment  of  which  provision  should  be  made. 
Where  separators  are  used  which  do  not  yield  a  middling  product 
two  machines  should  be  operated  tandem,  the  first  delivering  the 
magnetic  product  and  the  second  a  middling  product  and  non- 
magnetic discharge.  The  retreatment  of  middlings  should,  of 
course,  be  preceded  by  crushing,  and  where  the  ore  is  roasted  for 
magnetism,  a  reroast  may  also  be  necessary. 

CLEANING  MAGNETITE  CONCENTRATE 

In  the  separation  of  strongly  magnetic  minerals,  especially  on 
separators  of  large  capacity,  some  provision  should  be  made  for 
cleaning  the  magnetic  concentrate  from  entrained  particles  of 
waste.  Such  cleaning  is  accomplished  in  some  separators  by  sub- 
jecting the  concentrate  to  the  repeated  action  of  magnets  of  al- 
ternate polarity,  the  magnetic  particles  forming  loops  between  the 
poles,  which  loops  are  broken  and  remade  in  passing  from  one 
pole  to  the  next,  and  the  nonmagnetic  particles  allowed  to  fall. 
In  some  other  constructions  a  blast  of  air  or  jet  of  water  is  directed 
against  the  concentrate  while  held  by  the  magnets  and  the  en- 
trained particles  blown  or  washed  out.  Repeated  treatment  of  the 
magnetic  product  as  exemplified  by  the  Edison  deviation  separator 
accomplishes  the  same  result. 

TREATMENT  OF  FINE  MATERIAL 

In  crushing  ore  a  variable  amount  of  dust  or  slime  is  produced 
which  may  not  be  separated  advantageously  in  conjunction  with 
the  coarser  sizes.  No  especial  difficulty  is  met  in  the  separation 
of  strongly  magnetic  minerals  in  a  state  of  fine  division  either 
wet  or  dry;  several  wet  separators  are  designed  to  treat  ore  which 
has  been  reduced  to  slime.  The  separation  of  feebly  magnetic 
minerals  in  a  state  of  fine  division  is  a  more  difficult  problem,  as 
the  capacity  of  the  separator  is  cut  down  by  the  thinness  of  the 
ore  layer  which  may  be  treated. 

In  dry-crushing  plants   the  several  crushing  and  separating 


PRINCIPLES  OF   MAGNETIC  SEPARATION  15 

machines  are  usually  housed  in,  and  the  flying  dust  removed  from 
within  the  casings  by  exhaust  fans  and  settled  in  a  dust  chamber. 
Dust  is  a  source  of  danger  to  the  workmen  employed  about  the 
machines,  and  is  a  hindrance  to  the  separation  as  well. 

Electric  machinery  should  be  installed  in  a  separate  building, 
or  dust-tight  room,  as  magnetic  dust  collecting  on  magnetized  bear- 
ings, etc.,  and  on  motors  and  dynamos  is  troublesome. 

Nonmagnetic  dust  has  a  tendency  to  adhere  to  magnetic  con- 
centrate, which  may  be  a  source  of  loss,  notably  in  the  separation 
of  magnetite  and  apatite.  The  dust  may  be  removed  by  an  air 
blast,  or  if  the  trouble  be  aggravated,  resort  may  be  had  to  wet 
separation. 

If  the  separator  is  capable  of  fine  adjustment  and  the  ore  is 
accurately  sized,  fine  material  may  be  separated  readily,  the  capac- 
ity of  the  separator  becoming  less  the  lower  the  permeability  of 
the  magnetic  mineral  and  the  finer  the  material  treated. 

FEEDING  DEVICES 

A  usual  origin  of  separator  feed  is  some  form  of  roller  or 
reciprocating  feeding  device  placed  beneath  a  feed  hopper.  Such 
feeder  should  be  absolutely  automatic,  and  so  connected  with  the 
separator  mechanism  that,  should  the  separator  stop,  the  feeder 
will  stop  also.  The  feeder  should  spread  a  thin,  even  layer  of  ore 
upon  the  conveyor  belt,  shaking  plate,  drum  or  cylinder  employed 
to  transport  the  ore  to  the  separating  zones,  and  the  rate  of  feed 
should  be  capable  of  regulation.  The  feeder  should  be  so  con- 
structed that  if  a  large  piece  of  ore  or  other  material  should  find 
its  way  past  the  screening  apparatus  the  feeder  will  not  stop,  or 
necessitate  stoppage,  for  cleaning  out.  It  is  usual  to  place  a  screen 
at  the  feeder,  either  above  or  below  it,  which  will  eliminate  from 
the  feed  any  oversize  particles.  In  separators  which  employ  con- 
veyor belts  to  present  the  ore  to  the  magnet  the  feeder  should 
spread  a  uniform  layer  across  the  width  of  the  belt,  a  couple  of 
brushes  being  set  at  the  edges  of  the  belt  to  turn  back  toward 
the  center  any  particles  which  might  be  shaken  off  and  lost.  If 
a  feeder  works  poorly  and  does  not  distribute  a  uniform  ore  layer, 
a  piece  of  canvas  so  fastened  that  its  lower  end  will  drag  on  the 
conveyor  belt  will  be  found  useful  to  distribute  the  feed  properly. 


16  ELECTRO-MAGNETIC  ORE   SEPARATION 


ADJUSTMENTS 

A  magnetic  separator  should  be  capable  of  easy  adjustment 
to  suit  different  ores.  A  rheostat  should  be  provided  to  regulate 
the  current  on  each  magnet,  and  in  separators  in  which  the  ore  is 
introduced  between  the  poles,  the  distance  between  the  poles  should 
be  capable  of  adjustment.  The  amount  of  feed,  the  speed  at 
which  the  ore  is  presented  to  the  magnets,  and  the  distance  of  the 
ore  sheet  from  the  separating  poles  should  be  capable  of  regulation, 
as  well  as  the  positions  of  diaphragms  for  dividing  the  separated 
products. 

REQUIREMENTS  A  MAGNETIC   SEPARATOR   SHOULD   FULFILL 

Besides  the  ordinary  requirements  for  any  steadily  operating 
machine — such  as  automatic  operation,  economy  of  power,  dura- 
bility and  simplicity  of  construction,  and  visibility  of  working 
parts — a  magnetic  separator  should  be  provided  with  a  thin,  even, 
regular  feed  that  will  present  the  ore  at  proper  speed  as  close  as 
may  be  to  the  separating  poles  of  the  magnets,  which  should  have 
a  concentrated  and  homogeneous  field.  The  separator  should 
make  at  least  three  products;  magnetic  concentrate,  middling,  ancl 
nonmagnetic  tailing;  should  embody  some  provision  for  the  clean- 
ing of  the  magnetic  concentrate  from  entrained  nonmagnetic  par- 
ticles, if  of  high  permeability,  and  should  be  capable  of  complete 
and  accurate  adjustment. 

CAPACITY 

The  capacity  of  a  magnetic  separator  is  controlled  by  the  kind 
of  ore  treated,  by  the  percentage  of  magnetic  product  removed, 
and  by  the  size  to  which  the  ore  has  been  crushed.  The  effect  of 
the  size  of  the  particles  treated  upon  the  separator  capacity  is  well 
illustrated  by  the  results  obtained  at  Ems,  Germany,  in  the  re- 
moval of  raw  siderite  from  blende,  where  the  average  capacity  of 
a  Humboldt-Wetherill  separator  is  12  metric  tons  per  10  hours 
on  material  between  \  and  4  millimeters,  but  only  3.5  metric  tons 
per  10  hours  on  the  fines  passing  a  ^-millimeter  aperture.  In 
general,  the  more  strongly  magnetic  the  mineral  removed  the 
greater  the  capacity  of  the  separator.  The  Ball-Norton  belt  sepa- 


PRINCIPLES  OF   MAGNETIC   SEPARATION  17 

.-rator,  operating  on  magnetite  ore  crushed  through  6  mesh,  has  a 
capacity  of  about  20  tons  per  10  hours.  The  capacity  of  the 
Dings  or  the  Cleveland-Knowles  separator  may  be  taken  as  1  ton 
per  hour  on  roasted  pyrite-blende  concentrate  of  average  grade. 
The  above  figures  are  taken  from  representative  plants  and  are 
generalizations  only;  the  capacities  of  the  several  separators  are 
given,  when  it  is  possible  to  do  so,  in  the  descriptions  of  mills 
in  the  following  chapters. 

COST  OF  MAGNETIC  SEPARATION 

The  cost  of  magnetic  separation  consists  of  the  cost  of  pre- 
paring the  ore  for  treatment  plus  a  few  cents  per  ton  for  super- 
vision, excitation,  and  repairs.  When  the  ore  must  be  roasted  the 
cost  of  this  should,  of  course,  be  charged  against  the  separation 
of  which  it  is  a  prerequisite;  the  cost  of  roasting  pyrite  or  siderite 
to  the  magnetic  oxide  should  not,  under  average  conditions,  ex- 
ceed 50  cents  per  ton  in  a  well-equipped  plant  operated  at  capacity. 
Wherever  it  has  been  possible  to  do  so,  the  cost  of  treatment  has 
been  given  in  the  descriptions  of  mills  in  the  following  chapters. 

4 

TESTING 

Where  it  is  intended  to  employ  magnetic  separation  a  prelim- 
inary test  of  the  ore  is  even  more  important  than  with  other  proc- 
esses, on  .account  of  the  .difference  in  the  magnetic  behavior  of 
the  same  mineral  from  different  localities.  Most  manufacturers 
of  magnetic  separators  maintain  testing  establishments,  and  will 
make  small  scale  tests  without  charge  except  for  any  assaying 
that  may  be  desired.  Such  tests,  if  yielding  satisfactory  results, 
should  be  followed  by  a  large  scale  test  under  working  conditions 
and  personal  supervision.  While  it  is  impossible  to  standardize 
schemes  of  testing  to  suit  all  ores,  the  following  points  should  be 
covered:  (1)  An  accurate  sample  should  be  used,  sufficient  in 
amount  to  partake  of  the  nature  of  a  mill  run;  in  other  words,  to 
be  indicative  of  the  results  which  may  be  expected  from  commer- 
cial operation.  (2)  Determination  should  be  made  of  the  size  to 
which  the  ore  should  be  crushed  to  yield  the  best  results.  (3) 
If  there  is  a  choice  between  direct  separation  of  the  raw  ore  and 
separation  after  roasting  for  magnetism,  both  methods  should  be 


18  ELECTRO-MAGNETIC  ORE  SEPARATION 

tried  and  results  compared ;  which  might,  perhaps,  end  in  a  decision 
to  employ  a  combination  of  the  two  methods.  (4)  Separation  of 
the  ore  with  different  amperages  on  the  magnets,  different  belt  or 
drum  speeds,  etc.,  should  be  made  to  determine  the  adjustments 
necessary  to  attain  the  greatest  efficiency  and  capacity.  (5)  De- 
termination should  be  made  of  the  amounts  and  grades  of  all 
products  separately,  from  which  data  any  desired  combination  of 
results  may  be  computed.  (6)  Accounting  for  all  the  values  in  the 
feed  and  determination  of  the  sources  of  loss. 

PREPARATION  OF  THE  ORE  FOR  TREATMENT 

The  proper  preparation  of  the  ore  for  separation  is  as  important 
as  the  selection  of  the  best  method  of  treatment.  No  machine 
should  be  called  upon  to  treat  material  for  whose  separation  it 
was  not  intended.  The  cost  of  crushing,  sizing,  and,  where  neces- 
sary, the  cost  of  roasting  the  ore  in  preparation  for  magnetic 
treatment  is  many  times  as  great  as  that  of  the  actual  separation, 
and  the  original  outlay  required  for  equipment  is  usually  in  the 
same  proportion.  These  subjects  are,  with  the  exception  of  roast- 
ing for  magnetism,  fully  treated  in  all  the  standard  works  on  ore 
dressing,  but  a  discussion  of  some  of  their  features  must  be  con- 
sidered before  entering  upon  the  subject  of  the  methods  of  treat- 
ment of  the  different  ores  amenable  to  magnetic  separation.  The 
subject  of  roasting  for  magnetism  is  taken  up  in  the  chapters  de- 
scribing the  treatment  of  the  ores  to  which  it  is  applied. 

CRUSHING 

The  object  of  crushing  is  to  free  the  individual  minerals  in 
the  ore,  the  ideal  result  aimed  at  being  the  production  of  a  mixture 
of  particles,  each  of  which  is  composed  of  one  mineral  and  nothing 
else.  Such  a  result  is  never  attained  in  practice,  there  remaining 
always,  even  after  the  finest  comminution,  mixed  particles  consist- 
ing of  two  or  more  distinct  minerals. 

Ores  vary  widely  in  the  average  size  of  the  particles  or  crystals 
of  their  component  minerals,  and  while  one  may  liberate  the  bulk 
of  its  valuable  constituent  when  crushed  to  8  mesh,  another  ore, 
of  precisely  the  same  mineralogical  composition,  may  require  to 
be  crushed  to  30  mesh,  or  even  finer.  As  illustration,  at  Herrang 


PRINCIPLES  OF  MAGNETIC  SEPARATION  19 

the  ore  liberates  the  magnetite  when  crushed  to  8  millimeters, 
while  at  Pitkaranta  the  ore  is  slimed  before  separation,  which 
preparation  yields  but  44  per  cent,  of  the  magnetite  as  particles 
free  from  waste.  It  is  apparent  therefore  that  the  fineness  to  which 
an  ore  should  be  crushed  should  be  determined  carefully  in  each 
individual  case. 

The  best  way  to  arrive  at  the  size  to  which  any  particular  ore 
should  be  reduced  is  to  crush  and  test  a  sufficiently  large  sample 
of  it  to  be  indicative  of  the  results  which  may  be  expected  from 
treatment  on  a  commercial  scale.  The  ore  should  be  crushed  to 
a  size  determined  by  inspection,  or  by  actual  measurement,  of  the 
particles  of  the  valuable  mineral  and  objectionable  impurities  to 
be  eliminated,  and  should  be  sized,  separated,  and  the  several  prod- 
ucts from  each  size  assayed  separately.  The  coarsest  size  from 
which  a  considerable  proportion  of  clean  concentrate  may  be  sepa- 
rated and  a  clean  tailing  refused,  will  be,  in  general,  the  size  to 
which  the  preliminary  crushing  should  be  carried,  all  further 
crushing  being  carried  out  upon  the  middling  product. 

Graded  crushing  is  employed  to  minimize  the  amount  of  un- 
dersized particles  produced  in  reducing  the  ore  to  pass  a  given 
aperture,  the  ore  being  broken  in  two  or  more  stages,  and  the 
particles  already  fine  enough  screened  out  after  passing  each 
crushing  machine,  and  not  subjected  to  further  comminution.  The 
simplex  method  of  crushing  the  ore  in  one  operation  to  pass  a 
given  aperture  is  employed  where  the  production  of  a  large  amount 
of  undersized  material  is  not  counted  a  source  of  loss. 

In  mills  where  the  ore  is  to  be  separated  dry  the  question  arises 
whether  the  ore  shall  be  crushed  wet  and  then  dried,  or  dried  be- 
fore crushing.  In  the  latter  method,  which  is  extensively  employed, 
the  machines  should  be  housed  in  to  prevent  the  escape  of  dust 
into  the  atmosphere,  and  an  exhaust  fan  should  be  provided,  with 
connections  to  the  various  machines  and  a  settling  chamber,  or  bag 
house,  where  the  dust  may  be  collected.  The  dust  from  crushing 
ore  is  extremely  injurious  to  the  workmen  exposed  to  it,  and  every 
precaution  must  be  taken  to  prevent  its  escape  into  the  atmosphere 
of  the  mill.  The  workmen  are  required  to  wear  respirators  at 
many  plants  where  there  is  danger  from  so-called  lead  poisoning, 
and  also  are  shifted  from  one  position  to  another  in  order  to  re- 
duce the  danger  to  any  one  man. 


20  ELECTRO-MAGNETIC  ORE   SEPARATION 


SIZING 

While,  theoretically,  the  size  of  a  particle  of  magnetic  material 
should  have  no  effect  upon  the  attraction  of  a  magnet  for  it, 
results  from  practice  indicate  that  small  particles  are  more  easily 
influenced  than  large  particles.  It  is  difficult,  for  instance,  to 
separate  magnetic  minerals  from  each  other  when  the  more  weakly 
magnetic  mineral  is  present  as  the  smaller  particles.  Where  there 
is  a  wide  difference  between  the  magnetic  permeabilities  of  two 
minerals  in  a  mixture,  sizing  is  usually  unnecessary.  The  more 
closely  the  permeabilities  of  the  minerals  in  a  mixture  approach 
each  other  the  closer  must  the  sizing  be  carried  out,  and  ,the 
greater  the  number  of  sizes  treated  separately.  A  further  reason 
for  the  close  sizing  of  such  mixtures  is  -that  with  an  ore  layer  of 
evenly  sized  particles  closer  adjustment  may  be  made  in  the  dis- 
tance of  a  magnet  from  the  ore  stream.  In  most  instances,  with 
the  exception  of  the  separation  of  two  or  more  minerals  of  similar 
permeability,  a  reasonably  close  sizing  before  separation  gives  the 
best  results.  Sizing  of  the  finer  particles  produced  by  crushing 
is  easily  effected  by  water  classification,  but  as  the  ores  separated 
wet  usually  carry  magnetite  or  artificial  magnetite  as  their  mag- 
netic constituent  such  classification  is  rarely  necessary.  An  anal- 
ogous method  of  classification  has  been  extensively  adopted  in 
Europe,  where  a  current  of  air  is  employed  as  a  classifying  medium 
in  the  place  of  water. 

SPECIFIC-GRAVITY  CONCENTRATION 

The  concentration  of  ores  by  specific-gravity  methods  is  a  usual 
preliminary  to  magnetic  separation.  With  mixtures  which  require 
roasting  or  calcination  to  render  them  magnetic,  the  advantages 
of  such  preliminary  treatment  are  too  obvious  to  require  mention. 

DRYING,  COOLING,  ETC. 

In  dry  magnetic  separation  it  is  essential  that  the  ore  be  quite 
dry,  as  any  appreciable  moisture  causes  the  particles  to  adhere  to 
one  another  and  precludes  good  work.  Ore,  as  it  comes  from  the 
mine,  can  rarely  be  separated  without  drying,  still  less  the  products 


PRINCIPLES  OF   MAGNETIC  SEPARATION  21 

of  wet  concentration,  even  after  drying  in  the  air.  It  is  usual 
to  dry  the  ore  after  the  coarse  crushing  and  before  the  fine  classi- 
fication, as  moist  ore  clogs  the  screens.  Abroad,  a  scheme  for 
drying  the  ore  during  classification  has  been  successfully  carried 
out:  trommels  are  fitted  with  jackets  through  which  waste  steam 
is  passed,  and  the  ore  dried  as  it  passes  through. 

Care  must  be  taken  in  drying  ores  not  to  subject  them  to  suffi- 
cient heat  to  render  magnetic  any  minerals  which  are  not  in- 
tended to  go  into  the  magnetic  product;  in  the  case,  for  example, 
of  some  magnetic-blende  ores  carrying  pyrite,  a  quite  low  heat  is 
sufficient  to  form  a  film  of  magnetic  oxide  on  the  pyrite  and  render 
it  sufficiently  magnetic  to  be  attracted  by  the  intense  fields  em- 
ployed for  the  separation  of  magnetic  blende. 

Among  the  usual  forms  of  drying  furnaces  are:  (a)  The  re- 
volving cylinder  with  inclined  axis,  through  which  gases  from  a 
combustion  chamber  are  passed;  (b)  modifications  of  the  shaft 
furnace;  (c)  troughs  heated  from  without  by  steam  or  by  hot  gases 
flowing  through  them,  and  fitted  with  a  chain  or  other  conveyor 
to  transport  the  ore.  The  several  types  of  furnace  will  be  taken 
up  in  connection  with  the  plants  with  which  they  are  employed. 

Provision  should  be  made  for  cooling  roasted  ore,  and  in  some 
cases  ore  from  drying  furnaces,  before  allowing  it  to  come  into 
contact  with  belts,  etc.,  as  even  a  low  heat,  if  sufficiently  prolonged, 
will  cause  a  deterioration  in  the  materials  of  which  they  are  made. 
Expedients  resorted  to  for  cooling  ore  comprise  transportation  by 
conveyors  in  which  the  ore  is  stirred  and  exposed  to  the  air  until 
it  is  cool,  cooling  floors  upon  which  the  ore  is  spread,  contact  with 
cooled  surfaces,  water-jacketed  revolving  cylinders  and  others. 

With  separators  which  employ  high-intensity  fields  it  is  advis- 
able, and  often  imperative,  to  pass  the  ore  through  a  field  of  low 
intensity  to  remove  any  strongly  magnetic  particles  it  may  contain 
before  feeding  it  to  the  separator  proper.  Strongly  magnetic  par- 
ticles introduced  into  a  field  of  high  intensity  will  be  so  strongly 
attracted  as  to  tear  belts,  and,  if  in  sufficient  amount,  to  bridge 
across  between  the  poles  and  stop  the  separator. 


Ill 

SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS 

MANY  classifications  based  on  the  method  of  treatment,  on 
differences  in  construction,  etc.,  have  been  suggested  to  include 
the  different  types  of  magnetic  separators ;  separators  with  station- 
ary magnets,  and  those  whose  magnets  revolve ;  separators  in  which 
the  ore  is  attracted  directly  against  the  magnet,  and  those  which 
interpose  a  nonmagnetic  belt  or  drum  between  the  magnet  and 
the  particles  attracted ;  separators  which  lift  the  magnetic  particles 
from  the  mixture,  and  those  which  deflect  the  magnetic  particles 
from  a  falling  sheet  of  ore,  and  various  others.  The  classification 
of  most  value  is  that  based  upon  the  types  of  material  the  dif- 
ferent separators  are  suited  to  treat.  For  this  reason  the  only 
classification  attempted  here  is  to  distinguish  between  the  separa- 
tors designed  to  remove  ferromagnetic  minerals  and  those  designed 
to  treat  such  feebly  magnetic  minerals  as  raw  siderite,  limonite, 
etc.  A  number  of  separators  have  been  designed  to  treat  a  finely 
divided  feed  only,  and  others  for  use  as  cobbing  machines.  The 
sizes  of  feed  to  which  the  several  machines  are  suited  will  appear 
in  the  descriptions  of  the  individual  separators. 

Descriptions  have  been  published  of  a  large  number  of  sepa- 
rators whose  principal  claim  to  interest  is  an  historical  one;  the 
only  machines  here  described  are  those  which  are  at  present  of 
commercial  importance. 

THE  BALL-NORTON  BELT  SEPARATOR 

This  machine  employs  the  principle  of  a  series  of  magnets  of 
alternate  polarity  to  effect  a  thorough  turning  over  of  the  ore 
while  in  the  influence  of  the  magnetic  field,  thus  permitting  en- 
trained particles  of  waste  to  fall  from  the  concentrate. 

The  ore  is  fed  from  a  hopper  by  a  feed  roll  upon  a  horizontal 
belt  which  serves  to  present  it  to  the  magnets  from  beneath.  The 

22 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      23 

magnetic  particles  are  lifted  from  this  feed  belt  by  the  magnets 
and  held  against  a  take-off  belt  running  in  the  same  direction  and 
interposed  between  the  ore  stream  and  the  magnet  poles.  The 
take-off  belt  is  run  at  a  greater  speed  than  the  feed  belt  in  order 
to  carry  the  ore  past  the  magnets  in  a  thinner  layer.  The  belts 
are  made  of  rubber-covered  canvas,  and  means  are  provided  to 


P«rf  Hopper 


FIG.    1.— BALL-NORTON  BELT  SEPARATOR. 

alter  the  speed  of  belt-travel  to  suit  different  ores.  As  the  mag- 
netic particles  are  held  against  the  take-off  belt,  and  by  its  motion 
carried  past  the  poles  alternately  opposite  in  sign,  the  loops  of 
magnetic  particles  are  broken  and  reformed  as  they  pass  from 
one  pole  to  the  next,  permitting  entrained  particles  to  fall  from 
the  concentrate  into  a  tailing  compartment,  into  which  the  non- 
magnetic material  remaining  on  the  feed  belt  also  falls.  The 


24  ELECTRO-MAGNETIC  ORE   SEPARATION 

magnetic  concentrate  is  carried  past  a  partition  and  is  dropped 
from  the  last  magnet  into  a  separate  compartment. 

The  series  of  magnets  is  made  up  of  12  poles,  those  of  opposite 
sign  being  adjacent,  all  controlled,  in  the  type  machine,  by  one 
rheostat.  By  dividing  the  poles  into  two  series  by  suitable  con- 
nections, and  employing  an  additional  rheostat,  two  sections  of 
the  field  of  different  intensity  may  be  obtained. 

The  capacity  of  this  machine  is  from  20  to  35  tons  per  hour 
of  magnetite  ore  crushed  to  pass  a  J-in.  aperture. 

THE  "MONARCH,"  OR  BALL-NORTON  DOUBLE-DRUM  SEPARATOR 

This  machine  embodies  the  same  principle  of  magnet  construc- 
tion as  the  Ball-Norton  belt  separator.  It  consists  of  two  revolv- 


FIG.  2.— THE   BALL-NORTON   DOUBLE-DRUM   SEPARATOR. 

A,  Feed  hopper;  B,  tailing  compartment;  C,  middling  compartment;  D,  concentrate 
chute;  E,  magnets  of  which  the  adjacent  poles  are  of  opposite  sign;  F,  rougher  drum;  G, 
cleaner  drum. 

ing  drums  with  nonmagnetic  surfaces  placed  parallel  and  close 
together,  within  each  of  which  is  fixed  a  composite  electro-magnet 
made  up  of  adjacent  poles  of  opposite  sign. 

The  ore  is  fed  at  the  top  of  what  may  be  termed  the  rougher 
drum,  in  passing  around  which  the  nonmagnetic  particles  are 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS       25 

thoroughly  eliminated,  falling  into  a  hopper  below.  The  mag- 
netic particles  are  held  against  the  drum  by  the  magnets  within, 
and  while  passing  the  poles  of  opposite  sign  the  loops  of  magnetic 
particles  are  broken  and  reformed,  freeing  the  nonmagnetic  par- 
ticles, which  are  removed  by  a  combination  of  gravity,  centrifugal 
force,  and  the  effect  of  a  blast  of  air  impinging  upon  the  surface 
of  the  drum  in  a  direction  opposite  to  its  rotation.  At  a  point 
just  below  the  horizontal  diameter  of  this  drum  the  ore  passes 
beyond  the  influence  of  the  magnets  and  is  thrown,  by  centrifugal 
force,  against  the  face  of  the  adjacent  cleaner  drum  where  it  is 
caught  and  held  by  the  magnets.  The  cleaner  drum  revolves  at 
a  greater  speed  than  the  first  drum  encountered  by  the  ore  and  is 
furnished  with  weaker  magnets;  particles  of  inferior  permeability, 
which  were  held  by  the  rougher  drum,  are  here  thrown  off  into 
a  middling  hopper;  the  concentrate  is  carried  farther  and  thrown 
into  a  chute  after  passing  beyond  the  influence  of  the  last  magnet 
pole.  The  rougher  drum  makes  40  revolutions  per  minute  and  the 
cleaner  drum  50;  the  magnets  in  the  rougher  drum  take  10.5 
amperes  and  those  in.  the  cleaner  drum  13  amperes. 

The  capacity  of  this  separator,  with  drums  24  ins.  in  diam- 
eter by  24  ins.  face,  is  from  15  to  20  tons  per  hour  of  magnetite 
ore,  crushed  to  pass  16  or  20  mesh.  The  power  required  is  from 
£  to  |  H.  P.  for  operation,  and  from  1  to  1.5  E.  H.  P.  for  ex- 
citation. 

THE   DELLVIK-GRONDAL    SEPARATOR 

This  type  of  separator  was  designed  for  the  treatment  of  fine 
material.  It  consists  of  a  composite  electro-magnet  of  cylindrical 
form  which  revolves  about  a  vertical  axis.  This  cylinder,  of  cast 
iron,  carries  a  series  of  six  exciting  coils,  wound  in  circular  grooves 
cut  around  its  circumference.  These  coils  are  separated  from  each 
other  60  mm.,  and  are  so  wound  as  to  give  fields  of  progressively 
increasing  strength  from  top  to  bottom  opposite  the  iron  spaces 
between  the  coils,  which  form  the  separating  surfaces. 

The  ore,  in  suspension  in  water,  is  fed  from  a  launder  against 
the  topmost  magnetic  ring.  This  launder,  which  is  curved  to 
cover  about  90  degrees  of  the  magnetic  cylinder,  is  supplemented 
by  four  other  similar  launders  below  it,  which  serve  tp  catch  and 
return  against  the  drum  any  material  thrown  off  by  its  revolution. 


26 


ELECTRO-MAGNETIC  ORE   SEPARATION 


The  magnetic  particles  stick  to  the  rings  between  the  coils,  those 
not  held  by  the  first  ring  being  caught  and  held  by  one  of  the 
lower  rings,  each  of  which  has  a  field  of  greater  strength  than  the 
ring  next  above  it.  Nonmagnetic  particles  are  washed  from  the 
concentrate  by  a  stream  of  water  which  plays  against  the  cylin- 
der. By  the  revolution  of  the  cylinder  the  magnetic  particles 
adhering  to  it  are  carried  opposite  a  wooden  cylinder,  carrying 
secondary  magnets,  which  is  mounted  parallel  to  the  magnetic 
cylinder,  and  which  revolves  in  the  opposite  direction.  This 
wooden  cylinder  is  studded  with  a  number  of  iron  pegs  so  placed 


FIG.  3.— THE    DELLVIK-GRONDAL   SEPARATOR. 

A,  Feed  launder;  B,  splash  board;  C  C,  circular  launders  serving  to  present  the  ore  in 
suspension  in  a  stream  of  water  against  the  magnetized  cylinder;  D,  the  separating  cylinder; 
E,  exciting  coils;  F,  wooden  take-off  cylinder;  GG,  secondarily  induced  take-off  magnets; 
H,  tailing  launder;  /,  concentrate  launder. 

as  to  come  opposite  the  magnetic  rings  of  the  separating  cylinder. 
These  pegs,  distant  5  mm.  from  the  magnetic  rings,  concentrate 
the  lines  of  force  from  these  rings  upon  their  points,  giving 
rise  to  local  fields  of  greater  intensity  than  the  primaries,  and  so 
cause  the  magnetic  particles  to  leap  across  the  gap  and  attach 
themselves  to  the  pegs.  By  the  revolution  of  the  wooden  cylinder 
these  pegs  are  carried  beyond  the  influence  of  the  primaries,  lose 
their  secondarily  induced  magnetism,  and  drop  their  burden  of 
magnetic  particles,  which  removal  is  aided  by  a  stream  of  water. 
The  capacity  of  this  machine  is  from  30  to  45  metric  tons  per 
24  hours  of  magnetite  ore,  crushed  to  pass  a  1-mm.  aperture. 
The  magnets  require  6  amperes  at  31  volts.  The  separating  cylin- 
der makes  25  R.P.M.  and  the  take-off  cylinder  225  R.P.M. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS        27 


THE    GRONDAL    TYPE    II  SEPARATOR 

This  separator  consists  of  two  iron  disks  fastened,  60  mm. 
apart,  to  a  vertical  standard,  the  space  between  the  disks  being 
occupied  by  the  exciting  coils.  The  disks  and  coils  are  station- 
ary. This  circular  magnet  is  covered  with  a  brass  ring,  around 


FIG.  4.— THE   GRONDAL  TYPE   II  SEPARATOR. 

A,  Feed  hopper;  B,  feed  launders;  CC,  soft  iron  disks;  D,  exciting  coils;  E,  tailing  dis- 
charge; F,  concentrate  discharge. 

the  periphery  of  which  a  series  of  iron  strips  are  mounted;  and 
which  are  magnetized  from  the  disks  as  long  as  they  are  adja- 
cent to  them.  The  distance  between  the  disks  and  the  brass  ring 
is  so  varied  that  the  iron  strips  are  magnetized  during  one  half 
of  the  revolution  only.  The  ore  is  slimed  and  fed,  in  suspension 


28  ELECTRO-MAGNETIC  ORE   SEPARATION 

in  water,  against  the  brass  ring  through  launders  similar  to  those 
employed  in  the  Dellvik-Grondal  separator.  The  magnetic  par- 
ticles stick  to  the  iron  strips  during  half  the  revolution,  are 
thoroughly  washed  with  a  jet  of  water,  and,  on  passing  beyond 
the  influence  of  the  magnetic  disks,  are  washed  off  the  strips  by  a 
jet  of  water.  The  iron  strips  are  coated  at  the  top  with  a  layer  of 
lead  and  antimony.  This  layer  is  thickest  at  the  top  of  the  strip, 
gradually  shading  off  until  at  the  bottom  of  each  strip  the  ore 
comes  into  direct  contact  with  the  iron;  this  is  done  to  give  a 
field  of  steadily  increasing  strength  on  each  strip  in  the  direction 
of  passage  of  the  ore. 

THE    GRONDAL    TYPE    III    SEPARATOR 

This  separator  consists  of  a  fixed  electro-magnet  with  hatchet- 
shaped  pole  pieces  enclosed  in  brass  drums  which  revolve  at  80 
revolutions  per  minute.  The  surfaces  of  the  drums  are  fitted  with 
strips  of  iron  which  form  secondary  poles,  and  against  which  the 
magnetic  particles  are  attracted.  The  ore  is  introduced  into  a 
tank  beneath  the  revolving  drum,  which  is  suspended  just  above 
the  level  of  the  water;  the  sharp  edges  of  the  pole  pieces  give 
rise  to  a  concentration  of  the  lines  of  force  which  serves  to  lift 
the  particles  of  pure  magnetite  out  of  the  water  and  against  the 
drum,  where  they  stick  to  the  secondary  magnets  and  are  carried 
by  the  revolution  of  the  drum  out  of  the  field  and  discharged  into 
a  launder.  The  particles  forming  the  middling  product  are  not 
lifted  from  the  water,  but  are  sufficiently  attracted  to  separate 
them  from  the  waste  and  are  discharged  through  an  overflow  at 
the  side  of  the  tank.  The  nonmagnetic  particles  fall  to  the  bot- 
tom of  the  tank  and  are  discharged  through  pipes.  Generally  two 
drums  are  combined  in  a  twin  machine  which  requires  2  H.P.  for 
operation,  and  3.5  amperes  at  110  volts  for  excitation  of  the  mag- 
nets. The  capacity  of  this  machine  is  50  tons  in  24  hours. 

THE    GRONDAL    TYPE    IV    SEPARATOR 

This  type  of  separator  was  designed  to  deliver  magnetite  con- 
centrate as  dry  as  possible  from  a  wet  separation.  It  consists  of 
a  brass  disk  revolving  at  1450  R.P.M.  beneath  an  electro-magnet 
whose  pole  pieces  taper  to  an  edge  at  their  lower  extremities.  The 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS       29 


30 


ELECTRO-MAGNETIC  ORE  SEPARATION 


slimed  ore  is  delivered  by  a  launder  into  a  tank  beneath  the  brass 
disk,  and  the  magnetic  particles  are  drawn  up  against  the  disk, 
from  which  they  are  thrown  off  by  centrifugal  force  in  a  nearly 
dry  state.  About  1  H.P.  is  required  for  operation,  and  3.5 
amperes  at  110  volts  for  excitation  of  the  magnet. 

THE  GRONDAL  TYPE  V  SEPARATOR 

This  machine  consists  of  a  brass  drum  which  revolves  on  a 
horizontal  axis  and  encloses  a  series  of  magnets  of  alternate 
polarity  of  the  Ball-Norton  type.  The  difference  between  the 
working  of  this  machine  and  that  of  the  Ball-Norton  consists  in 


FIG.   6.— THE   GRONDAL  TYPE  V   SEPARATOR. 
1,  Feed;  2,  wash  water;  3,  concentrate;  4,  middling;  5,  tailing;  6,  magnets. 

feeding  the  finely  crushed  ore  in  the  former  case,  in  a  stream  of 
water  into  a  tank  beneath  the  separating  drum,  from  which  it 
is  raised  by  the  magnets  against  the  drum.  This  machine  re- 
quires 1  H.P.  for  operation  and  4  to  5  amperes  at  110  volts  for 
excitation.  It  is  said  to  have  treated  100  tons  of  crude  ore  in 
24  hours. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS        31 


FIG.   7.— THE   GRONDAL   SLIME   SEPARATOR. 
A,  Magnets;  B,  coils;  C,  settling  tanks. 


32 


ELECTRO-MAGNETIC   ORE   SEPARATION 


THE    GRONDAL    SLIME    SEPARATOR 

This  is  a  stationary  electro-magnet  with  two  beveled-edge  pole 
pieces  which  are  suspended  above  V-shaped  settling  tanks.  The 
slime,  in  suspension  in  water,  is  introduced  at  one  side  of  the 
tank  in  a  shallow  stream  which  flows  beneath  the  pole  pieces  to  a 
similar  discharge  at  the  opposite  side.  The  current  on  the  mag- 
net, which  is  suspended  close  to  the  water  level,  but  not  dipping 
into  the  water,  is  regulated  so  as  to  be  just  too  weak  to  lift  mag- 
netic particles  out  of  the  water.  The  magnetic  particles  form 


FIG.   8.— THE  WETHERILL  TYPE   F  SEPARATOR. 

A,  Magnet  poles;  B,  coils;  C,  tailing;  D,  middling;  E,  concentrate;  F,  rotating  arma- 
ture; Z,  feeding  device. 

bunches  in  the  water  beneath  the  pole  pieces  and  fall  to  the  bot- 
tom of  the  tank,  from  which  they  are  discharged  through  a  pipe. 
This  apparatus  is  frequently  employed  for  dewatering  the  pulp 
from  ball  mills,  in  which  case  a  stream  of  clear  water  is  intro- 
duced into  the  tank  at  the  bottom;  the  sand  falls  to  the  bottom 
and  is  discharged  through  a  pipe  along  with  the  bunches  of  mag- 
netic slime  collected  beneath  the  magnets.  By  regulation  of  the 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      33 

velocity  of  the  stream  of  pulp  and  the  amount  of  clear  water 
added,  the  size  of  particles  carried  over  the  waste  discharge  may 
be  adjusted  to  suit  the  ore  under  treatment. 

THE   WETHERILL   TYPE   F    SEPARATOR 

This  machine  comprises  a  separating  armature,  built  up  of 
alternate  disks  of  magnetic  and  nonmagnetic  material.  Upon  revo- 
lution between  the  primary  magnets  secondary  poles  are  set  up  at 


FIG.  4 


N 


FIG.  9.  — DETAILS  OF  MAGNET  ROLLER,  WETHERILL  TYPE  F  SEPARATOR. 

the  edges  of  the  magnetic  plates,  or  disks,  of  the  armature,  focus- 
ing the  lines  of  force  from  the  primaries  and  causing  magnetic 
particles  to  stick  to  the  armature  until  carried  beyond  the  influ- 
ence of  the  primary  poles.  The  waste  drops  off  the  armature  into 
a  receptacle,  while  the  magnetic  particles  are  held  until  the  neutral 
point  is  reached,  where  the  magnetism  of  the  disks  changes  from 
plus  to  minus,  when  they  fall  into  a  receptacle.  The  change  in 
magnetism  is  gradual,  so  that  by  means  of  suitable  partitions,  sev- 


34 


ELECTRO-MAGNETIC  ORE   SEPARATION 


eral  products  may  be  made  on  the  same  separator,  the  strongly 
magnetic  being  the  last  to  fall  from  the  armature. 

The  machine  is  built  in  one  size  only,  with  30-in.  poles,  but 
the  magnets  are  wound  for  various  strengths  of  current.  The 
capacity  of  the  machine  is  large:  the  makers  claim  that  400  tons 
are  put  through  these  machines  at  Mineville,  N.  Y.,  in  24  hours. 

THE    FROEDING    SEPARATOR 

This  separator  consists  of  a  round  table  of  brass  3  mm.  thick, 
and  1.45  meters  in  diameter,  which  slopes  from  center  to  circum- 
ference. Beneath  this  separating  surface,  which  revolves,  there  is 
a  system  of  12  stationary  magnets,  arranged  radially  to  cover  -J 


FIG.    10.— THE   FR  CEDING  SEPARATOR. 

A,  Magnets;  B,  revolving  table;   C,  tailing  discharge;    D,  concentrate  discharge;  E, 
wash  water  pipes. 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS      35 

of  the  surface  of  the  table ;  beneath  the  sector,  representing  •$-  of  the 
area,  there  is  a  gap  without  magnetic  attraction.  The  magnets  are 
of  alternate  polarity  and  have  their  corners  beveled  to  concentrate 
the  lines  of  force  at  the  periphery,  and  are  spaced  50  mm.  apart. 
Above  the  table  is  a  series  of  movable  perforated  pipes,  which 
deliver  a  spray  of  wash  water  on  the  ore  under  separation.  The 
ore  is  delivered  in  a  stream  of  water  at  the  center  of  the  table, 
and  spreads  out  in  a  layer  of  decreasing  thickness  toward  the 
periphery.  The  magnetic  particles  are  held  against  the  surface 
of  the  table  and  carried  by  its  revolution  to  the  sector  where 
there  is  no  magnet  and  here  washed  off.  The  nonmagnetic  par- 
ticles are  washed  off  the  table  by  the  wash  water  from  the  pipes. 
The  alternate  polarity  of  the  magnets  causes  the  magnetic  par- 
ticles to  turn  over  in  passing  from  one  magnet  to  another,  the 
entrained  waste  liberated  during  this  process  being  washed  off 
by  the  sprays  from  the  pipes,  which  are  hung  40  mm.  above  the 
table.  The  two  products  are  caught  in  separate  launders  at  the 
periphery  of  the  table.  Magnetic  particles  are  prevented  from 
being  washed  off  the  table  by  the  concentration  of  the  magnetic 
field  due  to  the  beveling  of  the  magnets  mentioned  before.  The 
capacity  of  the  machine  is  2  metric  tons  per  hour,  at  10  R.P.M. ; 
150  liters  of  wash  water  are  used  per  minute;  |  H.P.  is  sufficient 
to  operate  the  moving  parts,  while  the  magnets  require  8  amperes 
at  100  volts  for  excitation. 


THE    ERICKSSON    SEPARATOR 

The  construction  of  this  machine  is  best  understood  from  the 
accompanying  figures.  The  magnets  A  and  the  coils  C  revolve 
about  the  shaft  B.  The  magnet  wheels  are  divided  into  21 
spokes,  the  spokes  on  each  side  being  opposite  one  another.  Be- 
tween the  two  halves  of  the  magnet  is  an  annular  slot,  extending 
completely  around  the  circle;  the  walls  of  this  slot  are  thin  sheets 
of  nonmagnetic  metal,  and  this  space  is  filled  with  water  to  the 
height  of  the  axle.  The  ore  is  fed  by  a  stream  of  water  at  E ;  the 
magnetic  particles  form  bridges  in  the  fields  between  the  opposite 
spokes,  and  are  carried  around  by  the  revolution  of  the  magnets. 
At  K  a  launder  is  introduced  into  the  slot,  receiving  the  bridges 
of  magnetic  particles,  which  are  washed  out  of  the  machine 
through  this  launder  'by  a  strong  jet  of  water.  The  magnetic 


36 


ELECTRO-MAGNETIC  ORE   SEPARATION 


material  is  washed,  and  waste  particles  removed,  by  sprays  of 
water  playing  on  the  bridges  across  the  slot  between  the  time  it 
is  lifted  above  the  water  level  and  the  time  of  its  encountering 
the  discharge  launder.  The  nonmagnetic  particles  fall  to  the 
bottom  of  the  tank  and  are  discharged  at  H.  A  float,  J ' ,  is  con- 
nected with  the  discharge  opening,  H,  by  a  rod;  when  the  water 
rises  above  the  proper  level,  because  of  the  introduction  of  the 


Stop  Cook 


FIG.    11.— THE   ERICKSSON  SEPARATOR. 

A,  Revolving  magnet  spokes;  B,  axle;  C,  coils;  D,  separation  chamber;  E,  feed  launder; 
F,  slime  discharge;  G-K,  concentrate  discharge;  H,  tailing  discharge;  J,  automatic  dis- 
charge to  maintain  constant  water  level. 

feed,  the  discharge  gate  at  H  is  opened  and  the  surplus  water, 
along  with  the  waste,  flows  from  the  machine.  The  capacity  of 
this  separator  is  about  2  metric  tons  per  hour;  the  magnets  take 
20  amperes  at  110  volts.  Nonmagnetic  slimes  which  do  not 
settle  readily  are  drawn  off  from  time  to  time  through  the  pipe  F. 


THE    FORSGREN    SEPARATOR 

This  separator  comprises  five  independent  separating  zones 
which  may  be  employed,  if  desired,  on  different  ores  and  with 
different  strengths  of  field.  This  machine  consists  of  two  con- 
centric brass  rings  mounted  with  soft-iron  secondary  poles  at- 
tached to  a  spider  which,  by  revolution  about  a  vertical  axis, 
causes  the  rings  to  pass  between  the  poles  of  five  fixed  electro- 
magnets spaced  72  degrees  apart.  The  ore  is  fed  in  the  annular 


SEPARATORS   FOR    STRONGLY  MAGNETIC   MINERALS       37 

space  between  the  brass  rings  at  points  opposite  the  primary 
magnets;  the  magnetic  particles  in  the  ore  attach  themselves  to 
the  secondary  magnets,  while  the  nonmagnetic  particles  fall  past 
them  into  a  tailing  chute.  As  the  rotation  of  the  brass  rings 
carries  the  secondarily  induced  magnets  past  the  fixed  primaries 
they  lose  their  magnetism  and  the  attracted  particles  fall,  first 
the  feebly  magnetic  particles,  which  drop  into  a  middling  chute, 
and  finally  the  strongly  magnetic  particles  which  drop  into  a  con- 
centrate chute. 

From  J  to  3  H.P.  is  required  for  operation,  and  from  3  to  3.5 
amperes  for  the  excitation  of  each  primary  magnet.     The  capacity 


\ 


FIG.   12.  — THE    FORSGREN   SEPARATOR. 

A,  The  annular  space  in  which  the  separation  takes  place;  B,  tailing  discharge;  C,  mid- 
dling discharge;  D,  concentrate  discharge;  E,  coils;  F,  fixed  primary  magnets. 


of  this  machine  varies  with  the  size  of  the  material  treated: 
operating  on  magnetite  ore  crushed  to  1.2  mm.  it  handles  1| 
metric  tons  per  separating  zone  per  hour;  arranged  for  cobbing, 
it  handles  2.5  metric  tons  per  separating  zone  per  hour  for  sizes 
up  to  If  ins.  The  brass  rings  rotate  at  a  speed  of  from  5  to 
10  R.P.M. 


38 


ELECTRO-MAGNETIC  ORE   SEPARATION 


THE   EDISON    SEPARATOR 

This  machine  consists  of  a  series  of  bar  magnets  in  front  of 
which  the  ore  is  allowed  to  fall  in  a  thin  sheet.  The  magnetic 
particles  •  are  attracted  sufficiently  to  alter  their  trajectory  but 


/"  \ 

i\  I       Upper  Magnet  ~ 


He... 


\  [     Middle  Magnet    ]  j 
!  I  \          Headi          /  ll! 


\\  I      Lower  Magnet      I  /] 
IV '/ 

!,\\  X/i: 

'  I  \          Heads 

Final  Tailings 


Xailinga 


Tailings 


Tailings 


|i  [        4th  Magnet       [  y{ 

jX/v4\ 

//  s/        Nt  X^ 


Tailings 


ilinga 


FIG.    13.— PRELIMINARY   MAGNETS,  FIG.    14.— CLEANING   MAGNETS, 

EDISON   SEPARATOR.  EDISON    SEPARATOR. 


not  enough  to  draw  them  against  the  magnets.  The  falling  sheet 
thus  divided  is  caught  in  separate  chutes  or  hoppers.  The  current 
on  the  magnets  and  the  distance  from  the  falling  ore  sheet  to  the 
face  of  the  magnet  are  capable  of  adjustment  to  suit  different  ores. 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS        39 

A  single  magnet  may  be  employed  to  effect  the  separation,  or  a 
number  of  units  in  series.  In  the  mill  at  Edison,  N.  J.,  two 
systems  were  employed,  the  first  to  produce  a  clean  tailing 
product  and  a  second  for  the  cleaning  of  the  concentrate  from  the 
first  magnets. 

The  preliminary  magnets  are  arranged  as  shown  in  Fig.  13. 
The  ore  is  fed  past  each  end  of  the  magnets,  the  magnetic 
product  passing  from  the  machine  from  each  magnet,  while  the 
nonmagnetic  particles  are  successively  re-treated.  This  arrange- 
ment produces  a  clean  tailing  with  very  little  loss  in  magnetic 
material.  The  magnets  are  12  ins.  long,  4  ins.  thick  and  have 
a  separating  face  4  ft.  6  ins.  wide.  The  cores  are  of  cast  iron 
(as  the  magnets  are  never  saturated)  and  are  wound  with  No.  4 
copper  wire.  The  three  magnets  are  wired  in  series,  and  each 
has  a  different  winding,  the  upper  with  the  fewest  and  the  lower 
with  the  greatest  number  of  turns,  giving  separating  fields  of  con- 
stantly increasing  strength  in  the  direction  of  travel  of  the  ore. 
The  magnets  are  excited  by  15  amperes  at  80  volts.  The  capacity 
of  the  series  is  16  tons  per  hour  of  ore  crushed  to  pass  0.06  in. 
A  second  series  of  magnets  is  used  to  re-treat  the  magnetic 
product  from  the  above-described  machine  after  drying  and  re- 
crushing.  The  arrangement  is  the  same,  but  the  magnets  are  8 
ins.  long,  and  are  wound  with  No.  6  wire:  the  capacity  is  2.25 
tons  per  hour  on  material  crushed  to  pass  0.02  in.;  tailings  from 
the  last  magnet  are  waste.  These  magnets  take  10  amperes  at  120 
volts. 

The  cleaning  magnets  are  arranged  in  a  series  of  five  units, 
and  treat  the  concentrate  from  the  preliminary  magnets  after  the 
removal  of  dust.  With  this  machine  the  object  is  the  production 
of  a  clean  magnetic  product,  and  the  magnets  are  arranged  as 
shown  above  to  repeatedly  re-treat  the  magnetite,  the  tailing  being 
discharged  after  passing  each  unit.  The  magnets  are  4  ins.  long, 
2  ins.  thick  and  have  a  separating  face  4  ft.  6  ins.  wide.  They 
all  have  the  same  winding  of  No.  6  wire,  are  connected  in  series- 
and  take  17  amperes  at  100  volts.  The  tailing  from  the  upper 
magnet  in  this  series  is  run  to  waste,  while  the  tailing  from  the 
four  lower  magnets  is  regarded  as  middling  and  sent  back  for  re- 
treatment.  The  capacity  of  this  machine  is  about  0.9  ton  per 
hour. 


40 


ELECTRO-MAGNETIC  ORE   SEPARATION 


THE  EDISON  BELT  SEPARATOR 

This  machine  consists  of  a  belt  7  ft.  wide  which  travels  over 
two  pulleys  revolving  about  horizontal  axes  in  the  same  vertical 
plane.  Behind  the  side  of  the  belt  which  travels  upward  are 
placed  several  electro-magnets  staggered  across  the  belt,  adjacent 
magnets  being  of  opposite  polarity.  The  ore  is  fed  against  the 
belt  opposite  the  lowest  magnet,  the  magnetic  material  adheres 
to  the  belt  and  is  carried  upward  and  across  it  as  a  result  of 
the  arrangement  of  the  poles  of  the  magnets;  the  nonmagnetic 
particles  fall  from  the  belt.  The  material  fed  is  in  a  fine  state  of 
division  and  forms  tufts  on  the  surface  of  the  belt  which  turn 
over  and  over  in  their  passage  across  and  up  the  belt,  liberating 
any  particles  of  entrained  waste.  The  upper  magnet  extends 


FIG.   15.— THE  EDISON  BELT  SEPARATOR. 

further  toward  the  edge  of  the  belt  than  the  lower  magnets,  and 
the  magnetic  particles  are  dropped  from  it  into  a  series  of  small 
buckets  riveted  to  the  edge  of  the  belt,  and  so  discharged  from 
the  machine.  This  separator  is  designed  for  the  removal  of  non- 
magnetic particles  from  a  finely  divided  feed. 


BALL-NORTON  SINGLE-DRUM  COBBING  SEPARATOR 

This  machine  is  used  for  cobbing  ores  which  are  not  neces- 
sarily dry;  the  ore  fed  is  coarse  (1J  ins.)  and  the  separator  puts 
through  a  large  tonnage  with  the  idea  of  making  a  clean  concen- 


UNIVtKbll  Y     ] 

OF  ' 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS      41 

trate  of  the  pure  magnetite  pieces,  while  the  tailing  is  re-treated 
on  other  separators  after  crushing.  The  separator  consists  of  a 
drum  with  nonmagnetic  surface  which  revolves  about  a  composite 
magnet  in  the  form  of  a  sector  of  a  circle.  The  attraction  is 
exerted  by  16  electro-magnets  attached  to  a  spider  and  mounted 


Concentrates 


FIG.    16.— THE   BALL-NORTON  SINGLE-DRUM  SEPARATOR. 

on  the  shaft  of  the  drum.  The  magnets  are  stationary  and  cover 
a  little  more  than  180  degrees  of  the  circumference  of  the  drum. 
They  are  of  alternate  polarity,  which  causes  the  ore  to  turn  over 
as  it  is  carried  past  each  of  the  16  poles  by  the  revolution  of  the 
drum.  This  turning  over  permits  the  nonmagnetic  particles  to 
drop  off  the  drum  into  the  tailing  hopper.  The  ore  is  fed  near 
the  top  of  the  drum,  and  the  strongly  magnetic  pieces  are  carried 
past  the  tailing  hopper  and  thrown  off  by  centrifugal  force  as  they 
pass  beyond  the  influence  of  the  last  magnet,  falling  into  a  con- 
centrate chute.  The  amperage  is  regulated  so  as  to  pick  out  the 
pure  pieces  of  mineral  only,  allowing  composite  pieces  of  ore  and 
waste  to  go  into  the  tailing  to  be  separated  after  crushing. 

THE   WENSTROM    SEPARATOR 

This  machine  consists  of  a  drum  made  up  of  alternately  mag- 
netic and  nonmagnetic  bars,  which  revolves  about  a  horizontal  axis 
and  encloses  a  stationary  magnet.  The  stationary  magnet  is  cyl- 
indrical in  form  and  is  placed  eccentrically  within  the  revolving 


42 


ELECTRO-MAGNETIC  ORE  SEPARATION 


drum;  it  carries  four  circular  projections,  or  ridges,  between 
which  are  wound  the  exciting  coils,  so  connected  that  adjacent  pro- 
jections have  opposite  polarity.  The  surface  of  the  drum  is  made 
up  of  soft  iron  bars  with  nonmagnetic  spaces  between  them 
usually  filled  with  strips  of  wood.  The  bars  have  projections  from 
the  inner  surface  of  the  drum  which  engage  the  projections  from 
the  magnet,  making  them  practically  prolongations  of  the  poles  of 


FIG.  17.  — THE  WENSTROM  SEPARATOR. 

At  Fixed  electro-magnet;  B,  separating  surface  made  up  of  alternate  strips  of  iron  and 
wood;  C,  projections  of  magnet  which  engage  the  iron  strips  on  the  surface  of  the  drum;  D, 
exciting  coils;  E,  revolving  drum  carrying  the  magnetic  strips;  F,  feeding  chute. 

the  magnet.  The  projections  on  alternate  bars  engage  alternately 
the  north  and  south  poles  of  the  stationary  magnet,  giving  adja- 
cent bars  opposite  polarity.  The  projections  from  the  magnet  are 
cut  away  on  one  side  of  a  vertical  diameter  of  the  drum.  The 
ore  is  fed  at  the  top  of  the  drum  and  is  carried  forward  by  its 
revolution;  the  magnetic  pieces  are  held  by  the  magnetic  bars 
until  the  vertical  diameter  is  passed,  when  they  fall  into  a  hopper 
upon  the  bars  becoming  demagnetized.  The  waste  falls  into  a 
hopper  in  front  on  the  drum.  This  machine  is  designed  to  treat 
lump  ores  which  need  not  necessarily  be  dry.  It  is  made  in  two 
sizes:  the  larger  size  is  capable  of  separating  4-in.  lumps,  is  27  ins. 
in  diameter  and  24  ins.  across  the  face,  takes  15  amperes  at  110 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS   43 

volts  and  has  a  capacity  of  from  5  to  7  tons  per  hour.  A  smaller 
size  has  a  capacity  of  3  tons  per  hour  on  ore  1.5  ins.  maximum 
size. 

THE    NEW   WENSTROM    COBBING    SEPARATOR 

This  is  a  modification  of  the  machine  above  described.  The 
distance  between  the  ribs  making  up  the  surface  of  the  drum  of 
this  separator  is  varied  to  suit  the  size  of  the  ore  to  be  treated. 
For  the  finer  sizes,  from  -J  to  1J  ins.,  the  drum  is  covered  with 
a  sheath  of  German  silver.  For  treating  coarse  ores  the  drum  is 
made  in  diameters  from  2  ft.  10  ins.  to  3  ft.  4  ins.;  the  length 


FIG.    18.— THE   NEW  WENSTROM  COBBING  SEPARATOR. 

A,  Feeding  device;  B,  magnet  core;  C,  coils;  D,  projections  of  magnet  which  engage 
iron  strips  on  the  drum;  E,  revolving  surface  of  drum;  F,  tailing  discharge;  G,  concentrate 
discharge. 


of  the  drum  face  is  2  ft.  Eecently  some  of  these  machines  have 
been  built  with  twice  this  width  and  divided  into  two  sections, 
one  side  for  coarse  and  the  other  for  fine  material.  The  drums 
make  from  16  to  20  revolutions  per  minute;  the  electro-magnet 
requires  from  15  to  20  amperes  at  110  volts  for  excitation.  The 
capacity  of  this  separator  varies  from  5  to  10  tons  of  crude  ore 
per  hour. 

THE  GRONDAL  COBBING  SEPARATOR 

resembles  the  Wenstrpm  machine,  the  drum  being  made  up  of  ribs 
alternately  iron  and  brass.  The  former  are  £  in.  wide  and  the 
latter  -$5-  in.  wide.  The  drum  is  operated  at  a  speed  of  30  revo- 
lutions per  minute. 


44  ELECTRO-MAGNETIC  ORE   SEPARATION 


THE  PINGS  SEPARATOR 

This  separator  consists  of  an  inclined  shaking  conveyor  which 
serves  to  carry  the  material  to  be  separated  beneath  two  wheels, 
each  studded  with  secondarily  induced  magnets  and  revolving 
about  vertical  axes.  The  ore  is  fed  from  a  hopper  at  the  head  of 
the  inclined  conveyor,  and  is  transported  by  the  shaking  move- 
ment through  four  zones  of  separation,  due  to  the  magnet  wheels. 
The  first  magnet  encountered  by  the  ore  carries  the  less  current 
and  separates  the  strongly  magnetic  particles  only;  the  second 
magnet  carries  a  greater  current  and  separates  a  middling  product ; 
the  nonmagnetic  tailing  passes  off  the  end  of  ,the  shaking  con- 
veyor. 

The  conveyor  is  a  tray  made  up  of  a  sheet  of  ^  in.  steel  cov- 
ered with  asbestos  and  mounted  upon  hangers.  A  shaking  move- 
ment is  imparted  to  the  conveyor  by  an  eccentric,  the  movement 
being  upward  at  the  feed  end  and  also  in  the  direction  of  the 
travel  of  the  ore.  The  usual  speed  is  440  strokes  per  minute. 
While  passing  over  this  conveyor  the  ore  is  kept  constantly  in 
agitation,  thus  lessening  the  chance  of  entrainment.  The  con- 
veyor is  18  ins.  wide  and  7  ft.  long,  and  may  be  raised  or  lowered 
by  means  of  hand  wheels  on  the  hangers,  thereby  altering  its  dis- 
tance from  the  magnets.  By  raising  one  end  only,  a  different  and 
gradually  increasing  distance  from  the  plate  to  the  magnet  wheels 
may  be  obtained  at  each  of  the  four  zones  of  separation.  This 
separator  is  also  built  with  a  conveyor  belt  in  the  place  of  the 
shaking  conveyor. 

The  primary  magnets  are  fixed,  and  consist  of  two  steel  cores, 
which  carry  the  windings  and  connect  the  pole  pieces.  These  pole 
pieces  are  made  in  the  form  of  circular  arcs  to  correspond  with  the 
secondary  magnets  revolving  below.  The  secondary  magnets  are 
made  of  laminated  steel  and  are  disposed  around  the  periphery  of 
a  bronze  carrying  wheel  30  ins.  in  diameter ;  they  project  as  cylin- 
drical knobs  about  1  in.  below  the  carrier,  and  their  upper  ends 
are  U-shaped  to  engage  closely,  but  not  to  touch,  the  pole  pieces 
of  the  primary  magnets.  The  magnetic  circuit  is  completed 
through  the  steel  plate  beneath  the  asbestos  covering  of  the  con- 
veyor. As  the  individual  secondarily-induced  magnets  are  carried 
by  the  revolution  of  the  carrying  wheel  beyond  the  fields  of  the 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS      45 


primaries,  they  lose  their  magnetism  and  allow  the  attracted 
particles  to  drop  off.  These  magnets  reverse  their  polarity  be- 
fore entering  the  field  of  the  opposite  pole  of  the  primary,  caus- 
ing a  thorough  discharge  of  their  burden  of  magnetic  particles. 
Troughs  are  provided  to  carry  away  the  magnetic  particles 
dropped,  and  may  be  so  arranged  as  to  deliver  four  distinct 
products,  if  it  is  desired. 


FIG.    19.— THE   DINGS   BELT  TYPE   SEPARATOR. 

In  operation,  a  variety  of  adjustments  may  be  made,  to  suit 
different  ores,  by  altering  the  amperage  on  the  primary  magnets, 
by  changing  the  distance  from  the  conveyor  to  the  secondary 
magnets,  and  by  altering  the  inclination  of  the  conveyor.  The  ca- 
pacity of  the  machine  may  be  taken  at  1  ton  per  hour  of  properly 
roasted  blende-pyrite  concentrate.  About  one  mechanical  horse 
power  is  required  for  operation,  and  from  J  to  2  electrical  horse 
power  for  excitation. 


46  ELECTRO-MAGNETIC  ORE   SEPARATION 


THE    HUMBOLDT-WETHERILL    TANDEM    SEPARATOR, 
TYPE   VII 

In  this  a  broad  conveyor  feed  belt  transports  the  ore  to  be 
separated  beneath  highly  magnetized  rollers.  These  rollers,  which 
revolve  in  the  same  direction  as  the  travel  of  the  belt  beneath 
them,  pick  up  the  magnetic  particles  from  the  ore  stream  and 
deposit  them  on  cross  belts  which  remove  them  to  one  side.  At 
the  end  of  each  cross  belt  is  another  magnet  which  acts  upon  the 
magnetic  particles  as  they  are  thrown  off  the  cross  belt,  diverting 
them  into  suitable  receptacles,  according  to  their  permeabilities, 
giving  a  double  separation  of  the  magnetic  particles.  These  sep- 
arators may  be  operated  at  high  speed  and  are  said  to  have  a 
large  capacity  on  strongly  magnetic  ore  or  artificial  magnetite. 

THE    CLEVELAND-KNOWLES    SEPARATOR 

This  machine  comprises  a  conveyor  belt  which  serves  to  trans- 
port the  material  to  be  separated  beneath  two  cylindrical  electro- 
magnets which  revolve  about  vertical  axes  at  a  height  of  approxi- 
mately 1  in.  above  the  belt.  The  first  magnet  encountered  by 
the  ore,  usually  called  the  rougher  magnet,  is  the  weaker  of  the 
two  and  attracts  the  more  strongly  magnetic  particles  of  the  ore 
only;  the  second,  or  cleaner,  magnet  carries  a  higher  amperage  on 
a  greater  number  of  turns,  and  removes  such  magnetic  particles 
as  were  not  attracted  by  the  first  magnet,  making  a  middling 
product;  the  nonmagnetic  particles  pass  off  the  end  of  the  belt. 
This  machine  is  made  in  two  sizes,  with  12-in.  and  21-in.  belts 
respectively;  a  description  of  the  21-in.  belt  machine  will  serve  for 
both. 

The  belt  of  seamless  rubber  on  a  heavy  canvas  base  is  carried 
on  two  18-in.  pulleys  and  driven  from  a  line  shaft  through  the 
pulley  at  the  feed  end;  provision  for  taking  up  stretch  in  the 
belt  is  made  by  capstan  bolts  working  against  the  sliding  bearing 
of  the  pulley  at  the  discharge  end.  The  belt  is  kept  level  beneath 
the  magnets  by  three  liner  pulleys  which  are  capable  of  adjust- 
ment to  permit  the  regulation  of  the  distance  between  the  magnets 
and  the  surface  of  the  ore  stream. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      47 


48  ELECTRO-MAGNETIC  ORE  SEPARATION 

The  magnets  are  cylinders  26.5  ins.  in  diameter,  the  rougher  of 
cast  iron  and  the  cleaner  of  cast  steel  and  are  set  to  overhang 
the  belt  at  one  side.  An  annular  space  -J  in.  in  width  is  turned 
out  of  the  bottom  of  the  magnets  If  ins.  from  the  periphery  and 
is  filled  with  spelter;  the  magnetic  circuit  is  from  the  outside 
shell  across  the  spelter  gap  to  the  inner  core  of  the  magnet  about 
which  the  coils  are  wound.  The  magnetic  particles  are  attracted 
and  form  a  bridge  across  the  spelter  ring,  and,  by  the  revolution 
of  the  magnets,  are  carried  to  one  side  where  they  are  scraped  off 
by  a  brass  scraper. 

The  normal  speed  of  the  conveyor  belt  when  treating  artificial 
magnetite  is  100  feet  per  minute,  and  the  speed  of  the  magnets 
is  40  R.P.M.  At  this  speed  the  operator  is  capable  of  treat- 
ing 1  ton  per  hour  of  properly  roasted  blende-pyrite  concentrate 
of  average  grade  and  crushed  to  pass  4  mesh.  The  capacity  of  the 
12-in.  machine  is  about  one  half  that  amount.  The  amperage  em- 
ployed varies  with  the  ore  and  the  quality  of  the  roast  from  J  to 
2  amperes  on  the  rougher  magnet  and  from  3.5  to  10  amperes  on 
the  cleaner  magnet. 


THE    STERN-TYPE   WET    SEPARATOR 

This  separator  is  built  to  separate  wet  concentrates  and  finely 
divided  material.  It  is  said  not  to  require  a  preliminary  classi- 
fication of  the  feed,  and  to  work  well  on  very  finely  divided  ore. 
This  machine  consists  of  a  number  of  electro-magnets  mounted 
on  a  spider  which  revolves  in  a  tank  partly  filled  with  water.  The 
ends  of  the  revolving  magnets  are  connected  by  the  shaft  with  the 
walls  of  the  tank,  which  form  the  opposite  poles;  the  separation  is 
accomplished  in  this  space,  between  the  ends  of  the  moving  mag- 
nets and  the  cylindrical  wall  of  the  tank.  The  ore  is  fed  into  the 
machine  at  one  side,  the  moving  magnets  pick  up  the  magnetic 
particles  and  carry  them  above  the  water  level,  where  they  are 
washed  off  into  a  launder  by  a  strong  jet  of  water:  the  non- 
magnetic particles  are  drawn  off  through  the  bottom  of  the  tank. 
The  movement  of  the  magnets  through  the  water  stirs  up  the 
ore  thoroughly  and  permits  a  thorough  separation.  The  machine 
operates  on  a  0.5  H.P.  and  requires  10  amperes  for  excitation  of 
the  magnets. 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS      49 

I 


1* KZl 


50  ELECTRO-MAGNETIC  ORE   SEPARATION 


THE   PRIMOSIGH   WET    SEPARATOR 

In  general  principle  this  machine  resembles  the  Primosigh  sep- 
arator for  dry  ores  described  in  the  following  chapter.  The  mate- 
rial to  be  separated,  in  a  fine  state  of  division,  is  fed  in  suspension 
in  a  stream  of  water  into  the  grooves  at  the  top  of  the  magnet 


FIG.   22.  — THE   STERN-TYPE   WET   SEPARATOR.     SIDE   ELEVATION. 
A,  Revolving  magnets;  B,  tailing  discharge;  C,  concentrate  discharge. 

cylinder,  which  is  suspended  above  a  spitzkasten  so  as  to  be  im- 
mersed in  water  during  a  part  of  its  revolution.  The  nonmagnetic 
particles  drop  away  from  the  pole  pieces  as  soon  as  they  reach  the 
water,  while  the  magnetic  particles  are  carried  above  the  surface 
of  the  water  and  removed  by  a  series  of  secondarily  induced  magnet 
points  as  in  the  dry  separator.  This  machine  is  adapted  to  the 
treatment  of  fine  material.  Upon  a  feed  ranging  from  0.25  mm. 
down  to  dust  the  capacity  for  a  machine  with  four  separating 
grooves  is  0.4  metric  ton  per  hour.  Twelve  amperes  at  80  volts 
are  required  for  excitation,  and  J  H.P.  for  revolution. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      51 


THE   LEUSCHNER   TABLE    SEPARATOR 

This  separator  is  designed  to  treat  slime.  It  consists  of  a 
round  table  with  flat  surface  which  rotates  above  a  series  of  fixed 
electro-magnets.  The  magnetic  particles  are  held  against  the  sur- 
face of  the  table  by  the  magnets  beneath,  while  the  nonmagnetic 


FIG.   23.  — THE   HUMBOLDT  WET   SEPARATOR. 

slime  is  washed  off  by  jets  of  water.  Beneath  one  sector  of  the 
table  there  is  no  magnet  and  here  the  magnetic  particles  are 
washed  off  into  a  separate  launder. 

THE   HUMBOLDT    SINGLE-ROLLER    SEPARATOR:    FOR   WET 
SEPARATION 

This  is  similar  to  the  above-described  separator  for  the  treat- 
ment of  dry  ores.  The  drum  revolves  partly  in  water,  and  the  ma- 
terial to  be  separated  is  fed  against  it,  near  the  lower  vertical 


52 


ELECTRO-MAGNETIC  ORE  SEPARATION 


diameter.  The  nonmagnetic  particles  sink  to  the  bottom  while 
the  magnetic  particles  are  carried  farther  by  the  revolution  of  the 
drum  and  washed  off  by  a  stream  of  water.  A  stream  of  wash 
water  is  directed  against  the  magnetic  particles  while  held  against 
the  drum,  to  remove  nonmagnetic  dust  and  entrained  particles. 
The  drum  is  protected  by  a  water-tight  mantle  of  sheet  copper. 
The  capacity  of  these  machines  varies,  with  the  kind  of  ore  and 
the  size  treated,  from  500  to  4000  pounds  per  hour. 


THE   HERBELE   WET    SEPARATOR 

In  this  separator  a  series  of  electro-magnets  is  enclosed  in  a 
water-tight  casing.  An  endless  belt  travels  around  pulleys  at 
top  and  bottom  of  the  case  containing  the  magnets,  the  belt  mov- 


FIG.  24.— THE  HERBELE  WET  SEPARATOR. 

ing  downward  close  to  the  casting  on  the  side  of  the  ore  feed. 
This  apparatus  is  set  vertically  in  a  tank  filled  with  water  to  a 
point  above  the  top  of  the  magnets.  The  ore,  best  below  30  mesh, 
as  the  machine  is  intended  to  treat  fine  material,  is  fed  at  the 


SEPARATORS  FOR  STRONGLY  MAGNETIC  MINERALS      53 

top  of  the  belt  in  a  stream  of  water;  the  nonmagnetic  particles 
fall  and  are  carried  straight  down  by  the  flow  of  water,  while  the 
magnetic  particles,  held  against  the  belt  by  the  magnets,  are  car- 
ried around  the  lower  pulley  and  dropped  into  a  separate  hop- 
per. The  construction  is  best  understood  from  the  above  figure 
where  A  is  the  point  at  which  the  ore  is  fed,  in  suspension  in 
water;  B,  the  belt  which  conveys  the  magnetic  particles  past  the 
magnets;  c-c',  the  pulleys  about  which  the  belt  runs;  E,  the  con- 
centrate hopper ;  F,  the  concentrate  discharge ;  G,  the  tailing  hop- 
per; H,  the  tailing  discharge.  The  actual  separation  of  the  non- 
magnetic particles  vfrom  the  magnetic  takes  place  at  the  end  of  the 
shield  shown  close  to  and  opposite  the  lowest  magnet.  The  feed 
and  discharge  of  both  concentrate  and  tailing  are  continuous. 
The  belt  is  2  ft.  6  ins.  wide.  The  capacity  of  ihe  machine  reaches 
35  tons  per  24  hours. 

THE    ODLING    SEPARATOR 

In  this  machine  a  conveyor  belt  serves  to  carry  the  ore  beneath 
an  electro-magnet  whose  poles  extend  across,  and  just  above,  the 
conveyor  belt.  A  cross  belt  running  beneath  the  poles  carries  the 
magnetic  particles  attracted  against  it  to  one  side,  where  they  are 
discharged  into  a  chute.  The  nonmagnetic  particles  are  dis- 
charged off  the  end  of  the  conveyor  belt. 

THE  HUMBOLDT  SINGLE-ROLLER  SEPARATOR:  FOR  DRY 
SEPARATION 

This  machine  consists  of  a  drum  whose  face  is  made  up  of 
alternately  magnetic  and  nonmagnetic  bars,  revolving  about  fixed 
internal  electro-magnets.  The  primary  magnets  are  placed  to 
cover  a  part  of  the  lower  diameter  of  the  drum;  the  secondary 
magnets,  carried  on  the  face  of  the  drum,  become  magnetized  by 
induction  while  passing  the  primaries,  and  pick  up  the  magnetic 
particles  from  the  stream  of  ore  which  is  fed  beneath  the  drum. 
The  magnetic  particles  drop  off  the  drum  as  the  secondary  mag- 
nets become  demagnetized  on  passing  out  of  the  field  of  the 
primaries.  The  whole  machine  is  covered  with  a  dust-tight  hood. 
The  capacity  varies,  with  the  kind  of  ore  and  the  size  to  which 
it  is  reduced,  from  700  to  3000  pounds  per  hour. 


54 


ELECTRO-MAGNETIC  ORE   SEPARATION 


THE    FERRARIS    CROSS-BELT    SEPARATOR 

This  machine  comprises  a  series  of  six  inverted  horseshoe  mag- 
nets placed  in  line,  with  a  single  take-off  belt  running  immediately 
beneath  the  poles  of  all  the  magnets,  and  six  feed  belts  running 


FIG.   25.  — THE   HUMBOLDT  DRY   SEPARATOR. 

below  the  take-off  belt  and  at  right  angles  to  it,  each  feed  belt 
supplying  a  magnet.  The  poles  of  the  horseshoe  magnets  are  bent 
in  toward  each  other,  giving  a  concentrated  field  at  right  angles 
to  the  feed  belts.  The  magnets  are  fitted  with  an  iron  projection 
extending  a  few  inches  beyond  the  ends  of  the  poles  in  the  direc- 
tion of  travel  of  the  take-off  belt,  permitting  the  magnetic  particles 
to  be  carried  to  one  side  and  dropped  past  the  feed  belts  into  sep- 
arate hoppers.  Each  magnet  is  fed  with  a  different  size  of  ore 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      55 


56  ELECTRO-MAGNETIC  ORE  SEPARATION 

except  two  magnets,  which  both  treat  ore  passing  through  a 
1  mm.  screen,  as  this  size  preponderates.  Mounted  on  the  separa- 
tor frame  are  shaking  screens,  which  deliver  .sized  products  into 
separate  hoppers,  which  in  turn  deliver  on  to  the  feed  belts.  The 
feed  belts  are  12  ins.  wide  and  travel  1.5  ft.  per  second.  The 
height  between  these  belts  and  the  magnets  is  capable  of  adjust- 
ment through  the  small  guide  rollers  shown  just  below  the  mag- 
nets. The  distance  through  which  the  magnetic  particles  are 
lifted  varies  from  30  to  40  mm.  Each  magnet  requires  2  amperes 
at  50  volts.  The  capacity  of  the  apparatus  is  slightly  over  1 
metric  ton  per  hour. 


THE  FERRARIS  DRUM  SEPARATOR 

This  machine  comprises  a  shaking  conveyor  which  feeds  the 
material  to  be  separated  from  a  hopper  upon  a  conveyor  belt, 
which  in  turn  presents  it  to  a  magnetic  drum,  fitted  with  a  belt 
serving  to  remove  the  particles  attracted.  The  magnetic  drum  is 


FIG.   27.— THE   FERRARIS   DRUM   SEPARATOR. 

composed  of  a  series  of  composite  pole  pieces  which  dovetail  into 
xme  another  in  a  manner  best  understood  from  an  inspection  of  the 
accompanying  illustrations.  The  poles  are  insulated  by  a  filling  of 
zinc,  the  whole  forming  a  smooth  surface.  The  exciting  coils  are 
placed  within  the  drum,  connections  with  the  dynamo  being  made 
through  disks  which  dip  into  cups  containing  mercury.  This  ma- 
chine, fitted  with  a  belt  16  ins.  wide,  treats  about  500  kgm.  of 
calcined  limonite-calamine  ore  per  hour.  The  magnets  require  1.5 
amperes  at  110  volts  for  excitation. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      57 


THE   VIAL    SEPARATOR 

The  deviation  of  magnetic  particles  from  a  falling  sheet  of 
finely  divided  ore  is  the  principle  upon  which  this  separator  oper- 
ates. The  attraction  is  exerted  by  six  horseshoe  magnets  separated 
by  bronze  rings.  These  magnets,  which  are  arranged  horizontally, 
are  enclosed  in  a  brass  cylinder  which  revolves  at  from  8  to  10 
R.P.M.  The  ore  is  fed  in  a  thin  sheet  at  a  distance  of  from  5  to  25 
mm.  from  the  brass  cylinder.  The  magnetic  particles  are  drawn 
toward  the  magnets  but  are  prevented  from  adhering  to  them 
by  the  brass  cylinder;  the  magnetic  and  nonmagnetic  products 
are  divided  by  an  adjustable  diaphragm  and  fall  into  separate 
hoppers.  The  capacity  of  the  machine  is  500  kgm.  per  hour. 
The  entire  apparatus  is  enclosed  in  a  sheet-iron  housing  to  pre- 
vent air  currents,  which  would  interfere  with  the  separation. 
The  machine  treats  material  passing  a  screen  with  1.5  mm.  holes. 

THE  HEBERLE  DRY  SEPARATOR 

This  machine  consists  of  a  brass  drum  revolving  about  a 
series  of  fixed  electro-magnets.  The  ore  is  fed  against  the  drum 
at  a  horizontal  diameter.  The  nonmagnetic  particles  fall  past 


FIG.   28.— THE  HEBERLE   DRY  SEPARATOR. 

the  drum  into  a  hopper,  while  the  magnetic  particles  are  held 
against  the  surface  of  the  drum  by  the  magnets  and  are  carried', 
by  its  revolution  over  the  top  of  the  drum  to  fall  into  a  separate 
hopper.  The  drum  makes  36  R.P.M. .  6  to  7  amperes  at  65  volts 
are  required  for  excitation,  and  J  H.P.  for  revolution. 


58 


ELECTRO-MAGNETIC  ORE   SEPARATION 


THE   HUMBOLDT   RING   SEPARATOR 

This  consists  of  an  annular  magnet  suspended  in  a  horizontal 
plane  within  a  circular  casing.  The  ore  is  guided  to  the  magnet 
by  a  conical  shield,  and,  passing  between  the  magnet  and  the  cas- 
ing, the  magnetic  particles  are  drawn  inward,  while  the  nonmag- 
netic particles  fall  past  the  magnet  unaffected.  The  two  products 
are  gathered  in  two  concentric  inverted  cones,  the  inner  receiving 
the  magnetic  portion  and  delivering  it  from  the  separator  by 
means  of  a  spout  through  the  lower,  or  outer,  cone.  The  sep- 
arator contains  no  moving  parts.  In  lieu  of  an  air  gap  between 
poles  the  separation  is  effected  in  a  zone  of  dispersion  caused  by 


FIG.   29.— THE   HUMBOLDT  RING  SEPARATOR. 

Kt  Feed  cone;   M,  annular  magnet;   7,  shield  to  prevent  magnetic  particles  from 
adhering  to  magnet;  R,  the  space  in  which  the  separation  takes  place. 

a  narrowing  of  the  enclosing  casing,  which  induces  a  magnetic 
resistance.  The  operation  of  the  separator  is  best  understood  by 
inspection  of  the  figure  given  above.  The  magnetic  ring  has  a 
diameter  of  40  cm.,  or  a  separating  periphery  of  about  1.25 
meters.  The  separator  is  said  to  have  a  capacity  of  1  metric  ton 
per  hour.1 

1  "La  Separation  Electromagnetique  et  Electrostatique,"  D.  Korda,  p.  38. 


SEPARATORS  FOR   STRONGLY  MAGNETIC  MINERALS      59 


THE   KNOWLES    MAGNETIC    SEPARATOR 

This  separator  consists  of  a  stationary  primary  magnet  be- 
tween the  poles  of  which  a  belt,  which  is  studded  with  small  sec- 
ondary magnets,  is  caused  to  travel.  The  construction  is  made 
clear  in  the  accompanying  illustration.  The  ore  is  fed  from  a 


Side  Elevation 

FIG.  30. —  THE   KNOWLES   SEPARATOR. 


End  Vie\ 


A,  Guide  roller;  B  B,  poles  of  the  primary  magnet;  C,  driving  pulley;  F,  feed  hopper; 
E,  feed  plate;  I,  shaking  conveyor;  Z,  belt  studded  with  secondary  magnets;  S-P,  magnetic 
oscillator  for  vibrating  feed  and  conveyor  plates;  T  T,  discharge  guide  plates. 

hopper  upon  a  reciprocating  feed  plate,  which  in  turn  delivers  it 
upon  a  reciprocating  conveyor  plate;  this  conveyor  plate  brings 
the  ore  close  to  the  belt  carrying  the  secondary  magnets ;  the  plate 
and  belt  gradually  approach  each  other,  causing  the  ore  particles 
to  move  in  a  magnetic  field  of  constantly  increasing  strength. 
The  magnetic  particles  are  picked  up  by  the  secondary  magnets 
and  held  until  carried  past  the  primary  magnet,  when  they  are 
gradually  dropped  off  in  inverse  order  to  their  magnetic  per- 
meabilities ,by  the  gradually  decreasing  strength  of  the  secondary 
magnets.  The  nonmagnetic  material  falls  from  the  end  of  the 
conveyor  plate  into  a  separate  hopper.  The  upper  pole  of  the 
primary  magnet  is  beveled,  coming  to  an  edge  at  its  lower  end, 
thus  giving  a  concentrated  field  at  this  point:  the  lower  pole  is 
rounded,  and  being  movable,  an  adjustment  of  the  concentration 
of  the  magnetic  field  is  obtainable.  The  secondary  magnets  are 


60 


ELECTRO-MAGNETIC   ORE   SEPARATION 


soft-steel  rivets,  with  serrated  washers  on  the  lower  side  of  the 
belt,  there  are  about  200  of  these  rivets  per  square  foot  of  belt, 


Cfe 


Side  Front 

FIG.   31.  — DETAIL   OF   PRIMARY   MAGNET,   KNOWLES   SEPARATOR. 

copper  plated  to  prevent  rusting.  The  speed  of  belt  travel  is  250 
ft.  per  minute.  The  machine  is  designed  for  sizes  from  6  to  36-in. 
belt  width,  having  capacities  from  7  to  46  tons  per  24  hours. 


IV 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS 

WETHERILL-ROWAND     SEPARATOR     OR     WETHERILL     TYPE 

"E".  SEPARATOR 

THE  machine  consists  essentially  of  a  belt  which  conveys  the 
ore  between  the  poles  of  a  series  of  magnets,  so  arranged  that  the 
belt  traverses  the  air  gap  between  opposite  poles;  the  above  fig- 
ure illustrates  the  principle  of  this  separator.  The  lower  pole  of 
the  magnet  is  flat,  the  upper  pole  beveled.  This  arrangement 
causes  an  intense  concentration  of  the  lines  of  force  along  the 
lower  edge  of  the  upper  magnet,  and  the  direction  of  attraction 


FIG.  32.— SKETCH   SHOWING    PRINCIPLE   OF   WETHERILL-ROWAND    SEP- 
ARATOR. 

A,  Feed  hopper;  B-B' ,  conveyor  belt;  C,  coils;  D,  magnet  poles  ;  E,  cross  belts ;  F, 
nonmagnetic  discharge. 


of  a  magnetic  particle  presented  to  the  magnet  by  the  conveyor 
belt  directly  above  the  lower  pole,  is  upward  to  the  beveled  edge 
of  the  upper  pole.  A  cross  belt  traveling  beneath  the  upper  pole 
prevents  the  magnetic  particles  from  sticking  to  it,  and  carries 
them  to  one  side,  out  of  the  field.  In  order  to  free  the  mag- 

61 


62  ELECTRO-MAGNETIC  ORE   SEPARATION 

netic  particles  at  the  discharge  the  upper  pole  is  furnished  with  a 
tapering  iron  projection  in  the  direction  of  travel  of  the  cross  belts ; 
this  causes  a  gradual  reduction  in  the  strength  of  the  magnetic 
field  and  permits  the  magnetic  particles  to  be  removed  from  the 
field  and  drop  away  from  the  cross  belt  into  a  hopper.  Each 
magnet  in  this  construction  has  two  separating  zones ;  the  machine 
is  built  with  one,  two,  and  three  magnets  having  respectively 
two,  four,  and  six  separating  zones,  the  same  conveyor  belt  serv- 
ing all  of  them.  The  conveyor  belt  is  18  ins.  wide  and  the  cross 
belts  2  ins.  wide.  The  capacity  of  the  separator  depends  upon 


FIG.   33.— WETHERILL-ROWAND  SEPARATOR. 

A,  Feed  hopper;  B,  feed  roller;  C,  conveyor  belt;  D,  cross  belts;  E,  nonmagnetic 
discharge. 

the  depth  of  ore  feed  on  the  conveyor  belt  (which  must  be  very 
thin  to  prevent  entrainment),  and  upon  the  speed  of  the  con- 
veyor belt,  which  must  be  slow  enough  to  give  the  feebly  mag- 
netic particles  time  to  be  influenced  and  picked  up  by  the  mag- 
nets. The  speed  of  the  cross  belts  is  adjusted  to  take  care  of 
the  magnetic  material  picked  up  by  the  magnets.  The  ore  is 
fed  onto  the  conveyor  belt  from  a  hopper  by  means  of  a  feed 
roller  turning  inside  a  cylindrical  casing.  It  is  well  to  introduce 
a  coarse  screen  at  this  point  (or  before)  to  remove  large  pieces  of 
ore,  nails,  or  other  foreign  matter  which  may  have  passed  through 
a  leak  in  the  sizing  trommels,  as  any  large  piece  of  magnetic 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS         63 


material  will  tear  the  delicate  and  rapidly  moving  cross  belts  by 

pressing  against  them  under  the  attractive  force  of  the  magnets. 
The  windings  on  the  magnets  are  such  that 
the  second  magnet  encountered  by  the  ore  is 
stronger  than  the  first  and  the  third  stronger 
than  the  second,  permitting  the  recovery  of 
products  of  different  degrees  of  magnetic  per- 
meability. The  ore  stream,,  in  passing  the  mag- 
nets, has  a  tendency  to  gather  in  ridges,  simi- 
lar to  beach  sands  under  the  action  of  waves. 
These  ridges  may  be  smoothed  out  and  the  ore 
layer  prepared  for  the  next  magnet  by  means 
of  a  strip  of  heavy  canvas  placed  so  as  to  trail 
on  the  conveyor  belt.  Each  magnet  is  provided 
with  a  rheostat  to  control  the  exciting  currents. 
The  machine  is  capable  of  delicate  adjustment 
suitable  to  variations  in  the  ore  fed.  The 

capacity  of  the  E3  machine,  having  6  poles,  varies  from  J  to  4 

tons  per  hour,  depending  on  the  ore  treated. 

THE   HUMBOLDT-WETHERILL    CROSS-BELT    SEPARATOR 

This  is  practically  the  same  as  the  Wetherill-Rowand  separator 
as  built  in  the  United  States,  differing  only  in  details  as  to  the 
feeding  device,  construction  of  frame,  etc. 


FIG.  34. —CROSS 
SECTION  OF 
MAGNET  POLES, 
WETHERILL- 
ROWAND  SEPA- 
RATOR. 


FIG.  35.— HUMBOLDT-WETHERILL  CROSS-BELT  SEPARATOR. 


64 


ELECTRO-MAGNETIC  ORE   SEPARATION 


THE    MECHERNICH    SEPARATOR 

In  this  machine  the  separation  is  accomplished  in  a  field  be- 
tween two  cylindrical  poles,  of  which  the  upper  revolves  in  the 
direction  of  the  feed  introduced  between  them.  The  arrange- 
ment of  the  poles  is  shown  in  cross  section  in  the  figure  above.  In 
the  earlier  type-both  poles  were  cylindrical  and  both  revolved; 
in  the  later  machines  the  upper  is  the  separating  member  and 
the  lower  pole  is  stationary  and  covered  with  a  nonmagnetic  shell 
which,  revolving  in  the  direction  of  the  ore  feed,  serves  to  dis- 
charge the  nonmagnetic  particles  falling  upon  it.  The  feed  is 
introduced  against  the  upper  pole  as  shown  above;  the  feed  plate 
is  arranged  to  deliver  ore  automatically  by  means  of  a  bumping 
device ;  the  ore  is  pressed  against  the  pole  by  a  weak  spring  beneath 
the  feed  plate,  insuring  a  close  contact  between  the  ore  stream 
and  the  pole.  The  lines  of  force  are  concentrated  along  a  plane 


FIG.   36.— CROSS-SECTIONS   OF  MAGNETS,   MECHERNICH   SEPARATOR. 

A,  Feed;  B,  separating  pole;  C,  stationary  pole ;  D,  feed  plate;  E,  magnetic  concen- 
trate; F,  middling;  G,  nonmagnetic  discharge. 

passing  through  the  axes  of  both  poles;  in  other  words,  along 
the  line  where  they  are  nearest  together.  The  field  gradually 
decreases  in  strength  as  this  position  is  -left,  and  the  magnetic 
particles  drop  off  the  upper  pole  in  reverse  order  to  their  per- 
meability, as  by  its  revolution  they  are  carried  out  of  the  con- 
centrated field  toward  the  neutral  point,  90  degrees  away.  The 
nonmagnetic  particles  fall  from  the  upper  pole  immediately  upon 
leaving  the  feed  plate.  By  a  suitable  arrangement  of  plates  be- 
neath the  upper  pole  several  middling  products  may  be  made,  as 
well  as  the  magnetic  and  nonmagnetic  products.  Any  magnetic 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS 


65 


material  that  may  still  adhere  .to  the  pole  is  removed  near  the 
neutral  point  by  means  of  a  revolving  brush  of  steel  wires.  The 
exciting  coils  are  wound  on  the  cylinders  themselves.  The  pear- 
shaped  lower  pole  produces  a  greater  concentration  of  the  lines  of 
force  than  the  circular  section.  The  principal  function  of  the 


FIG.   37.  — MECHERNICH   SEPARATOR. 

A,  Feed  hoppers;  B,  separating  pole;  C,  stationary  pole;  D,  feed  plate;  E,  magnetic 
concentrate;  F,  middling;  G,  nonmagnetic  discharge. 

lower  pole  is  as  a  return  for  the  magnetic  flux.  The  machines  are 
usually  tmilt  double,  with  two  sets  of  poles.  The  whole  is  en- 
closed in  a  sheet-zinc  housing  to  prevent  the  escape  of  dust. 

The  machine  develops  a  field  of  high  intensity,  and  the  feed 
being  brought  into  close  contact  with  the  separating  cylinder 
(which  is  bare) /it  is  capable  of  separating  feebly  magnetic  min- 
erals. The  mechanical  and  magnetic  efficiencies  are  high.  The 
machine  is  built  in  two  sizes,  classified  according  to  the  length 
of  the  separating  poles,  respectively,  60  and  80  cm. 


THE   MOTOR-TYPE    SEPARATOR 

This  separator  consists  essentially  of  an  armature  revolving 
between  two  fixed  magnet  poles.  The  ore  is  fed  against  the  sep- 
arating roller  by  means  of  a  feed  plate  as  shown  in  the  above 
figure;  the  nonmagnetic  particles  fall  away  from  the  roller,  while 


66 


ELECTRO-MAGNETIC  ORE  SEPARATION 


FIG.  38.— DETAIL  OF  MAGNET  POLES  AND  ARMATURE,  MOTOR-TYPE  SEP- 
ARATOR. 

A,  Feed  plate;  B,  separating  armature;  C-C",  stationary  poles;  D,  magnetic  concen- 
trate; E,  middling;  F,  nonmagnetic  discharge. 


FIG.   39.  — MOTOR-TYPE  SEPARATOR, 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS         67 

the  magnetic  particles  are  carried  farther,  dropping  off  in  order 
inverse  to  their  permeabilities.  The  roller,  or  armature,  is  pro- 
tected by  a  copper  shell  which  revolves  with  it.  The  peculiarity  of 
this  separator  is  that  the  separating  roller,  or  armature,  is  set  in 
motion  by  the  current  supplied  to  the  magnets,  independent  of  any 
other  source  of  power.  The  length  of  the  separating  roller  is 
800  mm.;  the  power  consumption  is  from  60  to  100  watts.  The 
only  wearing  parts  of  this  machine  are  the  separating  surface  and 
the  automatic  feed  plate.  The  machine  is  completely  closed  in  to 
prevent  the  escape  of  dust  into  the  atmosphere  of  the  separating 
room. 

THE  PRIMOSIGH  SEPARATOR  FOR  DRY  ORES 

This  machine  consists  of  an  iron  core  or  shaft,  5,  upon  which 
six  sets  of  exciting  coils,  A,  are  mounted.  These  coils  are  pro- 
tected by  the  brass  rings,  0,  which  are  the  separating  surfaces. 
The  pole  pieces,  (7,  are  connected  with  the  core,  5,  by  iron  disks, 
and  it  is  in  the  groove  between  these  pole  pieces  that  the  sep- 
aration takes  place.  The  ore  to  be  separated  is  fed  from  hoppers 
through  chutes,  E,  into  the  grooves  between  the  pole  pieces  at  the 
top  of  the  rotating  magnets,  there  being  six  individual  separating 
zones,  each  equipped  with  its  own  feeding  device  and  take-off 
brush.  The  speed  of  the  rotating  magnet  cylinder  is  so  regulated 
in  conjunction  with  the  current  passing  through  the  coils  that  the 
nonmagnetic  particles  are  thrown  out  of  the  grooves  as  soon  as 
they  acquire  the  peripheral  speed  of  the  rotating  cylinder;  the 
weakly  magnetic  particles  are  carried  a  little  farther,  when  centrif- 
ugal force,  assisted  by  gravity,  causes  them  to  fall  into  suitable 
receptacles  placed  beneath  the  magnet  cylinder;  the  strongly  mag- 
netic particles  adhering  to  the  poles  are  removed  by  a  series  of 
secondary  poles  consisting  of  soft-iron  points  mounted  upon  brass 
disks,  L,  the  whole  revolving  in  the  direction  of  the  magnet  cylin- 
der. The  separator  requires  one  half  horse  power  for  revolution, 
and  from  14  to  15  amperes  at  80  volts  for  excitation.  The  capac- 
ity of  this  separator  is  about  1  metric  ton  per  hour. 


68 


ELECTRO-MAGNETIC   ORE   SEPARATION 


THE   ULRICH    SEPARATOR 

A  pair  of  electro-magnets,  between  the  wedged-shaped  poles  of 
which  a  separating  armature  is  revolved,  is  the  essential  feature 


FIG.  I.   Longitudinal  Section 


FIG.  2.  Cross  Section 


L'    ur 


FIG.  3.  Top  View 
FIG.    40.  — PRIMOSIGH   SEPARATOR. 

A ,  Coils;  B,  core;  C  C,  pole  pieces;  D,  separating  gap;  E,  feed;  L,  disk  carrying  secondary 
take-off  magnets;  O,  brass  rings  covering  coils;  F,  magnetic  concentrate;  GG,  middling 
products;  H,  nonmagnetic  discharge. 

of  this  machine.  This  armature  is  a  hollow  brass  cylinder  car- 
rying alternate  rings  of  iron  and  brass  J  in.  wide  and  held  close 
together.  This  cylinder,  or  armature,  is  three  ft.  long  and  makes 


SEPARATORS  FOR  FEEBLY   MAGNETIC  MINERALS         69 

50  R.P.M.  about  a  horizontal  axis.  Each  machine  carries  four 
separating  cylinders,  two  above  (on  the  same  axis)  and  two  below, 
the  upper  magnets  carrying  a  weaker  current  than  the  lower.  The 
ore  is  fed  from  a  hopper  by  a  distributing  arrangement  having  a 
feed  plate,  with  zigzag  channels  cast  in  it,  upon  the  top  of  the 
upper  cylinders.  Here  the  strongly  magnetic  particles  are  held  by 
the  concentrated  fields  at  the  edges  of  the  iron  rings,  and  de- 
flected into  a  receptacle;  the  material  passing  unaffected  over  the 
first  cylinder,  falls  upon  the  top  of  the  lower  cylinder  which  is 
revolving  in  a  stronger  field,  and  the  more  weakly  magnetic 
particles  are  removed  from  the  nonmagnetic  portion  of  the  feed, 
which  is  here  discharged  from  the  separator.  The  capacity  of 
these  machines  is  25  tons  per  24  hours;  they  require  1.5  E.H.P. 
and  1.5  M.H.P.  for  excitation  and  revolution,  respectively. 

THE   PAYNE   MAGNETIC    SEPARATOR 

This  separator  consists  of  two  drums  which  revolve  toward  each 
other  in  the  direction  of  the  passage  of  the  ore,  which  is  fed  be- 
tween them.  The  upper  drum  is  the  separating  member;  it  con- 


FIG.  41.  — DETAIL  OF  SEPARATING  SHELL,  UPPER  DRUM,  PAYNE  SEPARATOR. 

tains  a  stationary  electro-magnet,  placed  to  give  a  strong  field 
between  the  two  drums  along  the  line  where  they  are  closest  to- 
gether. The  revolving  shell  is  furnished  with  longitudinal  strips 
of  soft  steel  with  a  toothed  cross  section  as  shown  in  the  above 
figure.  The  magnetic  lines  of  force  are  concentrated  along  the 
ridges  of  these  teeth,  and  give  rise  to  a  field  of  sufficient  strength 
to  separate  weakly  magnetic  minerals.  The  lower  drum  is  also 
encased  with  a  revolving  shell,  and  serves  as  a  return  for  the  lines 


70  ELECTRO-MAGNETIC  ORE  SEPARATION 

of  force.  The  ore  is  fed  from  a  hopper  by  means  of  a  feed  roller 
upon  the  shell  of  the  lower  drum,  which,  by  its  revolution,  presents 
it  to  the  separating  drum ;  the  nonmagnetic  particles  are  discharged 
by  the  lower  drum,  while  the  magnetic  particles  are  picked  up  and 
held  on  the  ridges  of  the  upper  drum  until  carried  past  the  influ- 
ence of  the  magnet,  when  they  drop  off  into  a  hopper. 


THE   INTERNATIONAL   SEPARATOR 

This  machine  comprises  a  cylindrical  armature,  made  up  of 
thin  laminated  disks  of  annealed  wrought  iron,  which  revolves 
about  a  horizontal  axis  between  the  poles  of  an  inverted  horseshoe 
magnet.  The  disks  of  the  armature  have  saw-tooth  edges,  the 
teeth  being  staggered  on  adjoining  disks,  the  surface  of  the  arma- 
ture presenting  a  great  number  of  sharp  points.  The  pole  pieces 
of  the  magnet  are  recessed,  and  only  sufficient  space  is  left  between 


FIG.  42.  — DETAIL  OF  SEPARATING  ARMATURE,  INTERNATIONAL   SEPAR- 
ATOR. 


them  and  the  armature  for  the  passage  of  a  thin  layer  of  the  ore 
to  be  separated. 

The  lines  of  force  from  the  magnet  are  concentrated  upon  the 
points  of  the  armature,  giving  a  strong  field  capable  of  attracting 
weakly  magnetic  minerals.  The  magnetic  attraction  is  strongest 
at  a  point  on  the  horizontal  diameter  of  the  armature,  and  steadily 
decreases  from  this  point  around  to  the  vertical  diameter.  The 
ore  is  fed  at  the  top  of  the  armature,  and,  upon  being  carried 


SEPARATORS  FOR   FEEBLY  MAGNETIC  MINERALS 


71 


into  the  field  by  the  rotation  of  the  armature,  the  magnetic 
particles  adhere  to  the  points  of  the  saw  teeth,  the  nonmagnetic 
particles  sliding  off  into  a  hopper.  The  magnetic  particles  are 
carried  around  underneath  the  armature  and  drop  off  in  an  order 


FIG.    43.  — INTERNATIONAL   SEPARATOR. 

A,  Feed  hopper;  B,  separating  armature;  C,  magnet  poles;  D,  magnetic  concentrate;  E, 
middling;  F,  nonmagnetic  discharge. 


inverse  to  their  degrees  of  permeability.  At  the  vertical  diam- 
eter, where  the  magnetism  of  the  armature  changes  polarity,  even 
strongly  magnetic  particles  are  thrown  off  by  centrifugal  force. 
By  a  suitable  arrangement  of  dividing  planes  a  middling  product 
may  be  made  as  well  as  concentrate  and  tailing.  The  hoppers 
receiving  the  products  of  separation  are  adjustable,  and  may  be 
moved  according  to  the  products  it  is  wished  to  obtain.  The  posi- 
tion of  each  hopper  is  shown  by  indicators,  and  when  they  are  set 
at  the  desired  points,  may  be  clamped  in  place  by  set  screws.  The 
field  magnet  of  this  separator  weighs  9000  Ibs.,  the  whole  machine 


72 


ELECTRO-MAGNETIC  ORE   SEPARATION 


10,000  Ibs.  One  horse  power  is  used  for  excitation  of  the  magnet, 
and  one  horse  power  for  mechanical  operation.  The  capacity  of 
the  separator  is  from  2  to  4  tons  per  hour. 


THE   UBALDI    SEPARATOR 

This  machine  consists  of  an  iron  core,  in  the  shape  of  a  ring, 
carrying  exciting  coils  and  having  two  gaps  in  which  are  placed 
separating  armatures.  The  upper  pole  pieces  are  recessed  to  ad- 
mit the  armatures  and  the  lower  pole  pieces  are  tapered  to  con- 
centrate the  fields  at  the  separating  zones.  The  armatures  are 


FIG.    44.  — THE   UBALDI   SEPARATOR. 

1  and  2,  Separating  armatures;  3,  rounded  pole  piece;  4,  beveled  pole  piece;  5,  chute 
for  magnetic  particles;  6,  chute  for  nonmagnetic  particles;  7,  middling  chute;  8,  yoke  to 
control  relative  strength  of  fields;  10,  coils;  11,  core;  12  and  13,  pole  pieces. 

fitted  with  helical  ridges  which  serve  to  concentrate  further  the 
lines  of  force,  and  also,  by  revolution,  to  transport  the  attracted 
particles  to  one  side,  where  they  are  dropped  into  chutes.  The 
second  separating  zone  encountered  by  the  ore  is  stronger  than 
the  first,  permitting  the  machine  to  deliver  a  middling  product. 
The  lower  pole  piece  of  the  first  separating  zone  is  rounded,  caus- 
ing a  partial  concentration  of  the  lines  of  force,  while  the  lower 
pole  piece  of  the  second  separating  zone  is  beveled,  giving  rise 
to  a  more  complete  concentration  of  the  lines  of  force;  the  pole 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS 


73 


pieces  and  the  separating  faces  of  the  armatures  are  80  cm.  in 
length.  These  machines  require  1  H.P.  for  operation  and  have 
a  capacity  of  1200  kgm.  per  hour  on  leucite-bearing  lava. 


THE    HUMBOLDT-WETHERILL   TYPE   VI    SEPARATOR 

The  construction  of  this  machine,  which  operates  on  the 
principle  of  deviation  of  falling  particles,  is  best  understood  from 
the  above  illustrations.  One  pole  of  the  magnet  is  tapered  down 


FIG.  45.  — SHOWING  CONCENTRATION  OF  MAGNETIC  FIELD. 

to  a  fine  edge,  the  other  is  split  and  the  two  halves  carried  around 
the  coils  to  almost  meet  close  to  the  opposite  pole,  giving  an  in- 
tense field  (280  mm.  long).  The  ore  is  fed  from  a  hopper  by  means 
of  a  roller  upon  a  conveyor  belt  which  passes  around  a  small  pul- 


E    F     G 

FIG.    46.  — HUMBOLDT-WETHERILL   TYPE   VI   SEPARATOR. 

A,  Feed  hopper;  B,  feed  belt;  C,  coils;  DD,  magnet  poles;  #,  magnetic  concentrate; 
F,  middling;  G,  nonmagnetic  discharge. 

ley  close  to  the  field  of  separation.  A  second  belt  travels  about  the 
magnet  close  to  the  poles,  preventing  magnetic  particles  from  ad- 
hering to  them.  The  ore,  as  discharged  over  the  end  of  the  con- 
veyor belt,  passes  into  the  magnetic  field;  the  nonmagnetic 


74 


ELECTRO-MAGNETIC  ORE   SEPARATION 


particles  fall  straight  down,  while  the  magnetic  particles  are 
deflected  according  to  their  magnetic  permeability  into  different 
trajectories  and  are  caught  in  suitable  receptacles.  This  machine, 
removing  raw  siderite  from  a  feed  ranging  from  J  to  4  mm.  in 
size  of  grain,  fed  separately,  puts  through  0.6  metric  ton  per 
hour;  it  requires  from  8  to  9  amperes  at  90  volts. 

THE  WETHEKILL  PARALLEL  SEPARATOR 

This  consists  of  a  flat  conveyor  belt,  12  ins.  wide  and  15  ft. 
4  ins.  long,  between  the  centers  of  the  pulleys.  This  belt  runs 
horizontally,  at  a  speed  of  100  ft.  per  minute,  and  the  ore  is  fed 
on  it  in  an  even  layer  about  J  in.  thick.  At  a  distance  of  f  in. 


FIG.   47.  — WETHERILL   PARALLEL  SEPARATOR. 


above  the  top  of  the  belt  is  a  second  belt,  parallel  to  the  former 
and  running  in  the  same  direction.  This  second  belt  is  16  ins. 
wide,  extending  2  ins.  beyond  the  lower  belt  on  each  side;  it  runs 
at  a  speed  of  125  ft.  per  minute.  Above  the  upper  belt  are  two 
magnets  with  flattened  poles,  placed  close  together  with  the  line 
of  their  adjacent  edges  slanting  40  degrees  with  the  edges  of  two 
moving  belts.  The  magnetic  particles  are  lifted  from  the  lower 
belt  against  the  upper,  and  travel  with  it  and  across  it,  as  a  result 
of  the  diagonal  placing  of  the  magnets,  and  on  reaching  the  edge 
of  the  upper  belt  and  passing  beyond  the  magnets,  they  fall  past 
the  narrower  lower  belt  into  hoppers.  The  magnets  are  wound  to 
carry  6  to  8  amperes  at  52  volts.  The  machine  is  built  to  treat 
material  passing  a  16-in.  screen.  The  capacity  is  about  30  tons 
per  24  hours. 


SEPARATORS   FOR   FEEBLY   MAGNETIC   MINERALS         75 


THE  WETHERILL  HORIZONTAL  SEPARATOR 

This  machine  is  built  double,  with  two  magnets  and  four  pole 
pieces,  giving  two  separating  zones.  The  pole  pieces  are  beveled 
and  rounded  at  the  ends  to  a  £  in.  radius;  the  belts  pass 


FIG.    48.  —  WETHERILL   HORIZONTAL   SEPARATOR. 

A,  Coils;  B,  yokes;  C,  pole  pieces;  D,  canvas  feed  belts;  E,  hoppers;  F,  feeders;  G,  chutes; 
H,  guide  plates  for  discharge;  L,  tailing  hopper;  M,  concentrate  (magnetic  particles) 
hopper. 


76  ELECTRO-MAGNETIC  ORE   SEPARATION 

around  a  pulley  at  one  end  and  around  the  beveled  pole  piece  at 
the  other,  being  in  direct  contact  with  it.  The  poles  are  brought 
up  close  together  in  pairs,  the  beveled  edges  parallel.  The  con- 
struction is  made  clear  in  the  accompanying  plates.  The  ore  is 
fed  upon  the  belts  from  the  hoppers  in  a  sheet  from  J  in.  to  -f?  in. 
thick,  and  is  carried  around  the  beveled  pole  pieces,  at  which  place 
the  nonmagnetic  particles  fall  into  a  hopper,  and  the  magnetic 
particles  are  carried  a  little  farther  and  fall  into  other  receptacles. 
The  pole  pieces  are  10.75  ins.  wide  and  the  bevel  is  at  an  angle  of 
27  degrees;  the  opposite  pole  pieces  are  0.92  in.  apart  normally. 
This  arrangement  gives  an  intense  field,  and  the  ore  is  presented 
to  it  at  its  point  of  greatest  intensity.  The  adjustments  are  made 
between  the  speed  of  belt  travel,  the  current  on  the  magnets,  and 
the  distance  apart  of  the  poie  pieces.  This  machine  was  used 
to  treat  franklinite  ore  passing  0.058  in.  apertures  and  retained 
on  a  screen  with  0.01  in.  apertures:  it  treated  from  1.5  to  3  tons 
per  hour,  three  machines  in  series.  The  first  two  machines 
took  6  to  8  amperes  and  the  third  22  amperes  at  52  volts.  Two 
adjustable  guide  plates  below  and  a  little  to  the  side  of  each  sep- 
arating gap  are  used  to  divert  the  magnetic  and  nonmagnetic 
particles  into  their  respective  hoppers. 


THE  WETHERILL  INCLINED  SEPARATOR 

In  this  machine  the  ore  is  fed  upon  a  conveyor  belt  which  pre- 
sents it  to  a  magnetic  field  between  two  pole  pieces  similar  to  those 
used  in  the  horizontal  separator.  The  pole  pieces  in  this  machine, 
however,  are  set  at  an  angle  of  27  degrees  from  the  horizontal, 
the  plane  of  the  upper  pole  piece  being  1.2  ins.  above  that  of  the 
lower.  The  construction  is  made  clear  by  the  accompanying  illus- 
trations. The  ore  is  brought  by  the  conveyor  belt  as  close  as  pos- 
sible to  the  gap  between  the  pole  pieces ;  the  magnetic  particles  are 
here  lifted  off  the  conveyor  belt  against  belts  running  around  the 
ends  of  the  pole  pieces;  the  belt  of  the  lower  pole  is  the  dis- 
charge belt  for  the  concentrate,  which  is  carried  along  and  dropped 
into  a  hopper;  the  magnetic  particles  drawn  against  the  upper 
pole  are  carried  up  on  a  54-degree  incline  until  past  the  influence 
of  the  separating  zone,  when  they  fall  back,  and  by  their  momen- 
tum are  carried  past  the  gap  to  join  the  concentrates  on  the 


SEPARATORS  FOR  FEEBLY  MAGNETIC  MINERALS         77 

lower  belt.    The  magnets  are  wound  to  carry  from  6  to  8  amperes 
at  52  volts.     The  adjustments  are  made  between  the  distance  of 


FIG.   49.— WETHERILL   INCLINED   SEPARATOR. 

A,  The  coils;  B,  the  pole  pieces;  D,  discharge  belts;  E,  pulleys;  F,  feed  hoppers;  G, 
feeders;  //.conveyor  belt;  J,  adjustable  pulley  to  bring  conveyor  belt  close  to  separating 
gap;  L,  concentrate  hopper;  M ,  tailing  hopper;  X,  beveled  edges  of  pole  pieces. 

the  conveyor  belt  from  the  gap,  in  the  width  of  the  gap  between 
the  poles,  and  in  the  current  on  the  magnets.  These  machines, 
used  three  in  series  in  the  separation  of  franklinite  ores  passing  a 


78  ELECTRO-MAGNETIC  ORE   SEPARATION 

screen  with  0.01  in.  holes,  have  a  capacity  of  3.5  tons  per  hour. 
This  separator  is  built  double :  if  a  stronger  field  is  desired  a  yoke 
is  substituted  for  one  set  of  the  pole  pieces,  leaving  but  one  air  gap 
in  the  magnetic  series.  The  magnets  of  this  separator  are  wound 
the  same  as  those  of  the  horizontal  type.1 

1  "Richards  Ore  Dressing,"  p.  808. 


THE    CONCENTRATION    OF    MAGNETITE    ORES 

MAGNETITE  is  the  most  strongly  magnetic  of  all  minerals,  and 
it  is  therefore  natural  that  the  earliest  application  of  magnetism 
to  ore  dressing  was  for  its  concentration  from  gangue.  Magnetite 
ores  occur  in  large  bodies  in  almost  all  countries,  and  on  account 
of  the  high  iron  tenor  of  the  pure  mineral,  and  the  ease  with 
which  it  is  concentrated,  its  treatment  forms  one  of  the  most 
important  fields  of  magnetic  separation. 

Magnetite  (composition  Fe304)  has  a  specific  gravity  ranging 
from  5.0  to  5.1,  and  is  sufficiently  heavy  to  permit  of  its  con- 
centration from  gangue  by  specific-gravity  methods,  which  have 
had  an  extensive  application.  The  object  of  the  separation,  how- 
ever, is  twofold:  the  concentration  of  the  mineral  in  the  raw  ore 
to  a  product  of  sufficient  richness  for  the  blast  furnace,  and  the 
elimination  of  phosphorous  and  sulphur,  elements  which  fre- 
quently occur  with  magnetite  in  nature  and  which  enter  into 
combination  with  the  iron  in  the  furnaces  with  the  production  of 
an  inferior  metal.  The  specific  gravities  of  the  minerals  carrying 
these  objectionable  impurities  do  not  permit  their  complete  sep- 
aration from  the  magnetite  by  water  concentration.  The  high 
magnetic  permeability  of  magnetite,  which  is  65  per  cent,  of  that 
of  tempered  steel,  is  much  greater  than  the  permeabilities  of  these 
minerals  and  permits  a  separation  to  be  made  in  magnetic  fields 
of  low  intensity. 

The  results  from  the  several  separators  must  not  be  judged 
on  the  basis  of  the  percentage  of  iron  in  the  tailing  product,  as 
this  figure  is  controlled  largely  by  factors  other  than  the  efficiency 
of  the  separator.  Iron  ores,  to  be  commercially  profitable,  must 
carry  a  high  percentage  of  iron,  the  low  limit  being,  apparently, 
between  20  and  25  per  cent,  iron  present  as  magnetite.  This 
results  in  a  low  ratio  of  concentration  and  a  comparatively  small 
quantity  of  tailing,  and  a  large  percentage  of  iron  in  the  tailing 
may  represent  but  a  small  loss  when  compared  with  the  total  iron 

79 


80  ELECTRO-MAGNETIC  ORE   SEPARATION 

in  the  ore.  The  coarseness  of  the  crystallization  of  the  individual 
minerals,  the  presence  of  iron  in  nonmagnetic  form,  such  as 
hematite,  pyrite,  ferruginous  silicates,  etc.,  must  also  be  taken  into 
account,  while  the  grade  of  the  concentrate  aimed  at  is  also  an 
important  factor  in  determining  the  efficiency  of  the  separation 
in  terms  of  the  percentage  of  the  iron  in  the  original  ore  recov- 
ered as  concentrate. 

The  American  practise  tends  toward  the  production  of  the 
coarsest  size  concentrate  consistent  with  a  clean  separation  and 
reasonable  recovery,  employing  separators  which  treat  the  ore  dry. 
In  Sweden  it  is  customary  to  grind  the  ore  to  1  mm.,  or  even  finer, 
and  separate  on  machines  which  treat  the  ore  wet,  resorting  to 
briquetting  to  transform  the  concentrate  into  a  product  suitable 
for  the  blast  furnace.  These  differences  in  practise  are  largely 
due  to  the  coarser  crystallization  of  the  American  ores,  the  Swed- 
ish ores  being  more  often  made  up  of  minerals  in  a  fine  state  of 
division.  Magnetic  cobbing  has  been  successfully  applied  in  both 
countries,  and  produces  excellent  results  with  ores  which  carry 
magnetite  in  large  pieces,  and  in  which  apatite  and  pyrite  do  not 
interfere.  In  Sweden,  lump  ore  from  4  to  5  ins.  in  size  has  been 
cobbed  on  the  Wenstrom  separator  with  the  production  of  a  good 
concentrate,  and  the  separation  of  lumps  1.5  to  2  ins.  in  size  is 
regularly  carried  on  in  America  on  the  Ball-Norton  single-drum 
separator,  and  in  Sweden  on  the  Wenstrom  and  Grondal  cobbing 
machines. 

In  the  dry  concentration  of  magnetite  ores  the  fine  dust  formed 
by  crushing  is  often  a  source  of  loss,  but  is  not  so  counted  when 
some  of  the  newer  wet  separators  are  used;  in  Sweden  it  is  not 
unusual  for  over  40  per  cent,  of  the  ore  fed  to  the  separators  to  be 
fine  enough  to  pass  a  -|-mm.  opening. 

The  following  table  is  representative  of  the  best  practise  in  the 
magnetic  concentration  of  magnetite  ores  in  the  United  States  and 
Sweden. 

THE    ELIMINATION   OF   IMPURITIES 

The  objectionable  elements  occurring  with  magnetite  which 
are  wholely  or  partially  eliminated  by  magnetic  concentration,  are, 
in  the  order  of  their  importance,  phosphorus  as  apatite,  sulphur  as 
pyrite,  etc.,  and  titanium  as  menaccanite  or  ilmenite 

Apatite    (calcium  phosphate,  sp.  gr.  3.18  to  3.25)   is  usually 


THE  CONCENTRATION  OF  MAGNETITE  ORES 


81 


M 

i 

J- 

O 

.S 
'S 

!* 

•+J  ^ 

rH    t^ 

<N   05 

3 

o 

CO* 

^ 

O5 

co' 

CO 

h 

£ 

A  * 

S 

M 

to 

^_; 

i 

m 

i* 

g 

to   O 

co   co 

o 
3 

00 

8 

1 

rH 

I 

i 

I 

PH 

c 

o  o 

CO 

o 

0 

0 

0 

6 

0 

jj 

o 

I 

C 

to 

<M 

B 

«  ee 

9 

r— 

^2 

o 

rH 

a 

1 

*• 

• 

0 

o 

0 

0 

«    Q) 

0     rH 

CO    t> 

0 

to 

CO 

0 

<N 

(M 

CO 

rH     ^f 

r—   •HH 

j 

co 

1^ 

_' 

j^ 

Oi 

O5 

OH 

0   CO 

co   co 

CO 

CO 

CO 

•* 

co 

CO 

CO 

Id, 

•   <N 

§  s 

0 

J 

8 

8 

O 

0 

to 

0 

s 

1 

C 

rH    O 

rH 

0 

0 

•H 

0 

o 

0 

0 

• 
o 
p 

i« 

:  1 

8 

rH 

§ 

CO 

0 

£ 

;'   " 

0 

0 

(N 

0  « 

C   CO 

CO    >O 

0 

0 

(N 

0 

0 

00 

* 

3  § 

C5    CO 
»O    CO 

g 

C5 
CO 

i 

s 

CO 

§ 

00 
(M 

d 

gj 

n 

»o  •- 

.s  *** 

nbe    O 

.e 

H-* 

.s 

H-* 

a 

1 

a 

a 

a 

HH 

. 

. 

. 

0) 

. 

! 

* 

! 

1 

: 

• 

to 

i 

. 

w 

03 

C   S3 

3  3 

1 

63 

3 

63* 

3 

-o 

§ 

CO 

w 

-8 

6 
ig 

§ 

rH 

d 

• 

.  o   o 

O   ^ 

O 

O 

13 

'g 

3 

a 

13 

Cf-i 

tz  & 

^4       ^ 

Jxj 

*xj 

^o 

t^ 

*"O 

13  13 

"e8    O 

^ 

s 

§ 

o 

§ 

1 

1 

OQ   09 

CQ  S 

09 

05 

O 

s 

o 

o 

O 

0 

'| 

1-5 

»-9 

1 

s 

•    • 

•   ^ 

^ 

• 

| 

3 

*>  '> 

d 

1  ^ 

1 

i 

cto 
f 

. 

o' 

•  r—  ^ 

* 

1 

I  1 
3  i 

1     rl 

I 

1 

W 

02 

1 

~ 

cc 

i 

£ 

I 

3 


82  ELECTRO-MAGNETIC   ORE   SEPARATION 

feebly  magnetic,  though  not  sufficiently  so  to  be  picked  up  by 
magnetic  fields  of  low  intensity;  a  red  variety,  found  at  Mineville, 
N".  Y.,  is  sufficiently  magnetic  to  be  sometimes  drawn  into  the 
heads  by  the  Ball-Norton  separator.  This  mineral  is  a  common 
accessory  in  magnetite  ores;  it  is  quite  brittle,  and,  on  being 
crushed,  forms  a  fine  powder  which  has  a  tendency  to  stick  to 
the  magnetite  grains  and  so  find  its  way  into  the  concentrate. 
This  tendency  is  less  marked  when  the  concentration  is  carried  out 
in  water,  and  may  be  quite  thoroughly  overcome  by  the  use  of  a 
spray  of  wash  water  while  the  magnetite  is  held  by  the  mag- 
nets. In  dry  concentration  the  use  of  a  blast  of  air  directed 
against  the  minerals  held  by  the  magnets  is  .beneficial,  or  the 
employment  of  a  separator  which  turns  the  concentrate  over  and 
over  as  it  is  passed  from  pole  to  pole  of  opposite  sign. 

Apatite,  when  present  in  quantity  in  the  ore,  may  form  a  val- 
uable by-product,  as  it  may  be  worked  up  into  soluble  form  and 
sold  as  fertilizer.  At  Mineville,  N.  Y.,  the  Old  Bed  ores  carry 
from  1.35  to  2.25  per  cent,  phosphorus,  and  the  tailing  products 
find  a  market  for  their  phosphorus  content.  Two  grades  of  tail- 
ing are  made :  the  first  called  first  grade  apatite,  carries  3.55  per 
cent,  iron  and  12.71  per  cent,  phosphorus,  equivalent  to  63.55 
per  cent,  bone  phosphorus.  The  second  grade  apatite  carries  8.06 
per  cent,  phosphorus  and  12.14  per  cent,  iron,  or  an  equivalent  of 
40.30  per  cent,  bone  phosphate.  At  Svarto,  near  Lulea,  Sweden, 
the  ore  carries  up  to  3  per  cent,  phosphorus  as  apatite,  averaging 
1  per  cent.,  and  the  tailing  product  from  the  separators  carries 
13.7  per  cent,  phosphorus.  This  tailing  product  is  concentrated 
by  jigging,  and  after  fine  grinding,  is  treated  chemically  for  the  re- 
moval of  remaining  magnetite,  calcined  with  soda  ash  and  sold  as 
fertilizer  containing  30  per  cent,  phosphoric  acid  in  soluble  form. 

Concentrates,  to  be  acceptable  at  furnaces  which  turn  out  the 
best  grades  of  iron,  should  not  carry  more  than  .01  per  cent,  phos- 
phorus; ores  which  are  below  this  limit  command  a  premium.  As 
the  apatite  is  present  principally  in  the  waste  particles,  the  higher 
the  grade  of  concentrate  produced  the  lower  will  the  percentage 
of  phosphorus  be,  and  tests  should  be  made  on  the  ore  under  con- 
sideration to  determine  the  economical  limit  of  concentration  and 
elimination  of  impurities,  where  the  advantage  from  these  ceases 
to  offset  the  increased  loss  of  iron  in  the  tailing  due  to  the  in- 
creasing ratio  of  concentration. 


THE  CONCENTRATION  OF   MAGNETITE   ORES 


83 


Pyrite  (FeS2,  sp.  gr.  4.8  to  5.2)  is  a  common  accessory  min- 
eral in  magnetite  ores.  It  is  nonmagnetic  and  is  not  influenced 
by  the  most  intense  magnetic  fields;  it  is  easily  eliminated  in  the 
tailing  product  when  not  in  an  excessively  fine  state  of  division. 

Pyrrhotite  (Fe7S8,  sp.  gr.  4.5  to  4.65)  is,  on  the  other  hand, 
usually  ferromagnetic,  and  is  drawn  into  the  magnetite  concen- 
trate. It  is  not  so  strongly  magnetic  as  magnetite,  and  sometimes 
a  partial  elimination  is  accomplished;  but,  generally  speaking,  it 
may  not  be  removed  from  magnetite  by  magnetic  separation.  In 
the  case  of  some  complex  ores  carrying  pyrrhotite,  blende  in  a  fine 
state  of  division,  etc.,  the  sulphur  is  eliminated  by  roasting.  Mag- 
netite does  not  lose  its  magnetism  except  when  exposed  to  a  red 
heat  for  a  protracted  period,  and  such  roasting  may  be  carried  out 
either  before  or  after  separation.  Roasting  for  the  removal  of 
sulphur  is  practised  on  some  concentrates  produced  in  Sweden; 
the  heat  employed  in  briquetting  fine  concentrate  accomplishes  at 
the  same  time  an  elimination  of  the  sulphur. 

Another  objectionable  element  occurring  with  magnetite  is 
titanium  in  the  form  of  menaccanite  (sp.  gr.  4.5  to  5.0,  composi- 
tion the  same  as  hematite  but  with  varying  proportions  of  iron 
replaced  by  titanium).  This  mineral  is  magnetic,  but  not  to  so 
great  a  degree  as  magnetite ;  a  separation  of  magnetite  and  menac- 
canite may  be  accomplished,  but  only  at  the  expense  of  a  serious 
loss  of  iron  in  the  tailing  product.  Titanium  is  an  objectionable 
constituent  in  iron  ores  on  account  of  its  tendency  to  form  accre- 
tions in  the  blast  furnace.  Results  of  tests  made  to  eliminate  me- 
naccanite from  magnetite  will  be  found  in  the  following  table  of 
beach  sands,  in  which  the  minerals  occur  as  free  particles,  forming 
the  raw  material  for  separation : 

SEPARATION   OF   BEACH   SANDS' 


LOCALITY 

Per  cent,  Fe 

Per  cent.  Ti 

Cumberland,  R.  I   • 

Crude  sand. 

32  4 

6  25 

Concentrate.     .  .  . 

63  3 

2  36 

Tailing  

11  7 

8  76 

Crude  sand  

58  25 

8  46 

Concentrate  

68.45 

2  13 

Tailing  

33.3 

11  16 

Long  Island,  N.  Y  

Crude  sand  

48.49 

6  78 

Concentrate 

69  77 

trace 

Tailing  . 

36  22 

11  4 

1  Axel  Sahlin,  E.  &  M.  J.,  vol.  liii,  p.  664. 


84  ELECTRO-MAGNETIC  ORE   SEPARATION 


MAGNETIC    SANDS 

Many  attempts  have  been  made  to  exploit  beds  of  magnetite 
sands  concentrated  by  waves  and  streams  along  ocean  beaches  and 
banks  of  rivers.  Such  deposits  are  abundant  at  Moisie,  on  the  St. 
Lawrence,  and  in  smaller  developments  in  the  United  States  at 
Block  Island,  on  Long  Island,  along  the  Great  Lakes  and  on  the 
Pacific  Coast;  abroad,  deposits  in  Brazil  and  New  Zealand  have 
attracted  attention.  The  writer  is  not  informed  of  any  present 
commercial  operation  on  such  deposits;  magnetic  impurities  in 
the  sands  (menaccanite,  etc.)  and  the  unreliability  of  the  deposits 
due  to  their  mode  of  formation  have  probably  been  the  chief 
causes  of  failure. 

BRIQUETTING 

With  ores  which  require  fine  comminution  for  the  liberation 
of  the  magnetite  the  concentrate  produced  is  usually  briquetted, 
as  fine  concentrate  is  not  acceptable  at  the  furnaces.  While  the 
mill  at  Edison,  N.  J.,  was  in  operation  the  ore  was  crushed  to  pass 
^-in.  X  i  in.  openings,  and  the  concentrate  briquetted.  In  Swe- 
den the  briquetting  of  concentrate  is  usual. 

In  Sweden  the  plants  installed  by  The  Grondal  Kjellin  Co. 
have  been  very  successful.  The  fine  concentrate  is  pressed  into  bri- 
quettes without  the  use  of  binding  material,  the  moisture  in  the 
concentrate  being  regulated  to  obtain  briquettes  sufficiently  firm 
to  be  removed  from  the  press  and  loaded  onto  the  cars  used  in  the 
furnace.  These  cars  are  made  of  a  frame  covered  with  fire-brick 
and  have  a  tongue  cast  in  the  frame  at  the  front  end  and  a  groove 
at  the  rear  end,  and  along  the  sides  are  fitted  with  a  flange  which 
dips  into  a  groove  filled  with  sand  in  the  furnace,  a  string  of  these 
cars  thus  forming  an  air-tight  platform.  The  furnace  is  in  the 
form  of  a  tunnel,  with  track  running  down  the  center,  and  in  the 
middle  has  a  combustion  chamber  gas-fired.  The  air  needed  for 
combustion  is  admitted  beneath  the  gas-tight  platform  at  the  feed 
end  of  the  furnace,  and,  passing  the  discharge  end,  returns  above 
the  platforms  of  the  cars  with  their  loads  of  briquettes,  enters  the 
combustion  chamber,  whence  the  products  of  combustion  continue 
above  the  platform  to  an  outlet  near  the  feed  end  of  the  furnace. 
The  cool  air  circulating  beneath  the  platform  keeps  the  wheels  and 


THE  CONCENTRATION  OF  MAGNETITE  ORES 


85 


framework  of  the  cars  cool,  becomes  heated  as  it  at  the  same  time 
cools  the  burned  briquettes,  and  enters  the  combustion  chamber 
hot;  the  hot  gases  in  turn  heat  the  briquettes  and  are  themselves 
cooled  before  they  are  liberated  from  the  furnace.  Owing  to  this 
application  of  the  regenerative  principle  the  thermal  efficiency  of 
the  furnace  is  good,  the  gases  escaping  at  a  temperature  of  less 
than  100°  C.  and  the  consumption  of  coal  averaging  7  per  cent,  of 
the  weight  of  briquettes  burnt,  the  principal  loss  in  heat  is  the 


FIG.   50.  — GRONDAL  BRIQUETTING  PLANT,  SWEDEN. 

evaporation  of  the  water  in  the  briquettes.  The  temperature  in 
the  combustion  chamber  reaches  1,300°  or  1,400°  C.,  and  at  this 
heat  the  particles  agglutinate  sufficiently  to  make  a  firm,  hard 
briquette  which  will  stand  rough  usage.  The  time  consumed  by 
the  operation  varies  with  the  ore  treated  and  the  degree  of  desul- 
phurization  required;  any  sulphur  in  the  concentrate  is  readily 
eliminated. 

Briquettes  may  be  made  at  a  lower  temperature  through  the  use 
of  various  binding  materials:  at  Pitkaranta,  Finland,  3  to  5 'per 
cent,  lime  is  added  to  the  concentrate  which  is  then  briquetted,  and, 
after  being  allowed  to  set  for  two  weeks,  heated  to  800°  C. ;  at  Edi- 
son, N.  J.,  briquettes  were  made  with  a  resinous  binder.  Where  no 


86  ELECTRO-MAGNETIC  ORE   SEPARATION 

binder  is  used  the  only  requirements  are  a  proper  proportion  of 
coarse  and  fine  particles  to  avoid  excessively  large  interstitial 
spaces,  and  a  sufficiently  high  heat  to  sinter  the  magnetite 
particles.  It  has  been  estimated  (P.  McN.  Bennie)  that  the  cost 
of  briquetting  under  conditions  obtaining  in  the  Eastern  United 
States  would  be  45  cents  per  ton. 

At  Mineville,  New  York,1  there  are  extensive  magnetic  concen- 
tration works  built  by  Messrs.  Witherbee,  Sherman  &  Co.  for  the 
treatment  of  ores  from  their  mines.  The  ores  are  of  two  classes: 
the  New  Bed  and  the  Harmony  ores  carry  from  40  to  69  per  cent, 
iron  as  magnetite  and  are  low  in  phosphorus;  the  Old  Bed  ores 
are  high  in  phosphorus,  carrying  from  1.35  to  2.25  per  cent. 
The  apatite  varies  in  color  and  in  the  size  of  crystals;  that  with 
a  deep  red  color  develops  magnetic  qualities  of  sufficient  strength 
to  carry  some  free  crystals  into  the  concentrate;  it  also  adheres 
to  the  crystals  of  magnetite  in  a  more  marked  degree  than  the 
green  or  yellow  varieties.  The  yellow  crystals  break  away  freely 
from  the  magnetic  material.  When  the  magnetite  is  in  large  pieces 
in  the  crude  ore,  or  in  large  crystals,  it  is  readily  handled  by 
cobbing;  when  the  ore  is  massive,  or  when  the  magnetite  and 
apatite  crystals  are  small  and  intimately  associated,  finer  crush- 
ing is  necessary  for  the  same  degree  of  concentration.  The  ore 
from  the  Harmony  Mines  is  cobbed  on  a  Ball-Norton  single-drum 
separator,  and  magnetite  recovered  in  large  pieces,  the  waste  going 
for  finer  crushing  and  further  magnetic  treatment  to  Mill  No.  1. 

The  cobbing  plant  is  near  the  "  B "  shaft  of  the  Harmony 
Mines,  the  skips  dumping  into  a  chute  which  feeds  a  30-  X  18-in. 
Blake  crusher  weighing  29  tons.  The  crusher  is  driven  from  a 
jack  shaft  which  is  belted  to  a  General  Electric  induction  motor 
of  100  H.P.  operating  at  440  volts.  The  ore  is  crushed  to  1^  ins. 
and  is  conveyed  from  the  crusher  by  a  20-in.  Robins  belt  conveyor 
to  a  bin  over  a  Ball-Norton  single-drum  separator.  After  passing 
through  the  separator  the  cobbed  material  and  tailing  fall  on 
separate  20-in.  belt  conveyors  and  are  transported  up  an  incline 
to  storage  bins.  These  two  conveyors  are  operated  by  a  rope  drive. 
The  cobbed  product  and  the  tailing  storage  bins  are  placed  over 
and  alongside,  respectively,  two  tracks  upon  which  standard-gauge 
hopper-bottom  cars  run,  connecting  with  mill,  railroad  and  wharves. 
The  cobbed  product  is  called  "  Harmony  cobbed  " ;  it  is  a  coarse 
1 J.  H.  Cranberry,  E.  &  M.  J.,  vol.  Ixxxi,  p.  1082. 


THE  CONCENTRATION  OF   MAGNETITE  ORES 


87 


magnetite  with  little  gangue,  and  carries  about  61  per  cent,  iron; 
it  is  used  to  mix  with  lower-grade  ores  at  the  furnaces,  where  it  is 
desirable  on  account  of  its  coarseness  and  uniform  grade.  The 
tailing  carries  sufficient  magnetite  to  be  crushed  and  concentrated 
in  Mill  No.  1. 

Mill  No.  1  treats  crude  ores  from  the  "  A  "  shaft  of  the  Har- 
mony Mine  and  the  tailing  from  the  cobbing  plant.  The  ore  is 
weighed  and  dumped  into  a  storage  bin  which  feeds  a  30-  X  18-in. 
Blake  crusher  working  at  250  R.P.M.  After  passing  through  the 


FIG.   51.  — MILL  NO.    1,   MINEVILLE,   NEW  YORK. 

crusher  the  ore  is  screened  to  }-in.,  the  fines  going  directly  to  a 
dryer,  while  the  oversize  is  passed  through  a  size  H  Gates  crusher, 
after  which  it  also  goes  to  the  dryers. 

The  dryer  is  built  of  4-  X  6-  X  12-in.  furnace-brick.  The  ma- 
terial slides  over  cast-iron  tees  5  ins.  wide  on  top  and  with  a  shal- 
low stem  arranged  in  horizontal  rows,  six  in  a  row,  with  the  rows 
6  ins.  apart,  vertically.  The  bars,  in  vertically  adjacent  rows,  are 
staggered.  Six  rows  parallel  to  and  underneath  each  other  are 
followed  by  six  similar  rows  at  right  angles  to  the  first;  this  ar- 
rangement obtains  from  the  top  to  the  bottom  of  the  stack.  The 
dryer  is  made  with  a  bridge  wall  and  an  outside  furnace.  The 
gases  from  the  furnace  divide  at  the  bridge  wall,  part  passing  up 
the  chimney  and  part  into  the  shaft.  There  are  two  openings 
from  the  shaft  into  the  chimney,  which  serve  to  permit  the  gases 


88  ELECTRO-MAGNETIC  ORE   SEPARATION 

to  pass  from  one  to  the  other,  which  tends  to  raise  the  capacity 
of  the  dryer  by  reason  of  the  eddying  effect  set  up. 

From  the  dryer  the  material  is  fed  to  a  Ball-Norton  single- 
drum  separator.  The  concentrate  from  this  machine  goes  to  a 
shipping  bin  and  the  tailing  through  a  set  of  Anaconda  rolls, 
40  X  15  ins.,  with  Latrobe  steel  shells,  operating  at  50  R.P.M. 
Thence  the  ore  is  elevated  and  passed  over  a  f -in.  tower  screen  from 
which  it  is  fed  to  two  Ball-Norton  belt-type  separators  which  make 
concentrate,  a  shipping  product  carried  to  bins  on  a  Eobins  belt 
conveyor,  and  tailing  which  passes  to  two  other  separators  of  the 
same  type  but  operating  with  a  stronger  current.  These  cleaning 
separators  remove  the  iron  to  the  economical  limit,  and  the  tailing 
here  produced  is  conveyed  to  a  waste  dump.  The  iron  product  of 
the  cleaning  separators  is  crushed  in  Eeliance  rolls  36  X  14  ins. 
fitted  with  Latrobe  steel  shells  and  operating  at  100  R.P.M.  The 
final  cleaning  is  effected  on  two  other  separators  of  the  same  type, 
the  magnetite  product  is  carried  to  shipping  bins  by  a  20-in.  belt 
conveyor,  and  the  tailing  to  the  dump  upon  an  11-in.  belt  conveyor, 
which  handles  all  the  tailing  from  this  -mill.  The  power  supply 
for  this  mill  comprises  four  Crocker- Wheeler  50  H.P.  direct-cur- 
rent motors,  operating  at  220  volts,  and  a  75  H.P.  General  Elec- 
tric motor  also  employed. 

Mill  No.  1  has  a  capacity  of  800  tons  of  crude  Old  Bed  ore 
per  day,  or  of  600  tons  of  Harmony  or  New  Bed  ore ;  both  figures 
are  for  10  hours.  Of  the  feed  77  per  cent,  is  recovered  as  con- 
centrate. A  table  of  average  results  follows: 


MATERIAL 

Iron 
Per  cent. 

Phosphorus 
Per  cent. 

Lean  Harmony  ore 

50  26 

0  292 

Harmony  concentrate  

64  10 

0  133 

Harmony  tailing  . 

13  97 

0  877 

Mill  No.  2  treats  the  Old  Bed  ore,  which  is  high  in  phosphorus. 
The  treatment  here  is  similar  in  many  points  to  that  in  Mill 
No.  1,  and  the  points  of  difference  only  will  be  described.  The 
power  is  furnished  by  three  60  H.P.  General  Electric  motors, 
form  K,  operating  on  440  volts.  A  10  H.P.  motor  of  the  same 
type  is  used  to  drive  the  conveyors  to  the  shipping  bins.  The  mill 


THE  CONCENTRATION   OF   MAGNETITE   ORES  89 

is  divided  into  the  crushing,  the  separating,  and  the  re-treating 
plants,  each  of  which  divisions  is  independent  as  to  power  sup- 
ply; each  motor  is  arranged  to  control  the  machinery  and  con- 

FLOW  SHEET  FOR  MILL  NO.   1 
Ore  from  mine  and  cobbing  plant 

storage  bin 
30  in.  X  18  in.  crusher 

|  in.  screen 
through  oversize 

Gates  H  crusher 

I 


dryer 

Ball-Norton  single-drum  separator 
[coarse  concentrate]  tailing 

40  in.  X  15  in.  rolls 
elevator 

f  in.  screen 

| 

Ball-Norton  belt  separator  Ball-Norton  belt  separator 

[concentrate]  tailing  tailing  [concentrate] 


Ball-Norton  belt  separator  Ball-Norton  belt  separator 

[tailing]  [middling]  middling          [tailing] 

36  in.  X  14  in.  rolls 


Ball-Norton  belt  separator  Ball-Norton  belt  separator 

[tailing]  [concentrate]  [concentrate]  [tailing] 

veyors  without  reference  to  the  others.    Between  each  two  divisions 
bins  are  installed  having  storage  capacity  for  a  two-hours'  run. 

The  Wetherill  Type  F  separator  is  working  on  the  same  ma- 
terial as  the  Ball-Norton  belt  separators.  The  Wetherill  Type  E 
separators  treat  the  tailing  crushed  to  10  and  16  mesh,  from  the 


90 


ELECTRO-MAGNETIC   ORE   SEPARATION 


main  battery  of  separators  and  make  three  products.    The  first  belt 
removes  any  magnetite  liberated  by  the  secondary  crushing,  which 


is  re-treated  on  a  Ball-Norton  belt  separator,  which  makes  a  ship- 
ping concentrate  and  tailing.     The  second,  third  and  fourth  belts 


THE  CONCENTRATION   OF   MAGNETITE   ORES 


91 


make  a  hornblende  product,  which  also  carries  the  magnetic  apatite 
mentioned  as  sometimes  being  found  in  these  ores.  The  nonmag- 
netic discharge  from  these  separators  is  called  first  grade  apatite, 
consisting  of  apatite  with  pure  white  silica.  The  magnetite  product 
from  Mill  No.  2  averages  65  per  cent,  iron  and  higher.  The  plant 
is  arranged  to  re-treat  this  concentrate  and  produce  a  magnetite 
carrying  in  excess  of  71  per  cent,  iron,  which  is  sometimes  made 
to  supply  the  demand  for  the  manufacture  of  the  so-called  "  mag- 
netite "  electric  lamps.  The  mill  has  a  capacity  of  800  tons  of 
Old  Bed  ore  in  10  hours.  A  table  showing  the  average  analyses  of 
the  crude  ore  and  products  of  this  mill  for  a  year's  run,  together 
with  the  approximate  amounts  of  the  several  products,  follows : 


MATERIAL 

Amount 
daily,  tons 

Iron 
Per  cent. 

Phosphorus 
Per  cent. 

Bone  Phos- 
phate, perct. 

Crude  ore  Old  Bed 

800 

59.59 

1.74 

Old  Bed  Concentrate  
First-grade  apatite.    .  .  . 

.       680 
60 

67.34 
3.55 

0.675 
12.71 

63.55 

Second-grade  apatite  .... 

60 

12.14 

8.06 

40.30 

The  other  elements  in  the  Old  Bed  concentrate  are,  silica,  2.2 
per  cent. ;  manganese,  0.08  per  cent. ;  alumina,  0.90  per  cent. ;  lime, 
3.14  per  cent.;  magnesia,  0.31  per  cent.;  sulphur,  trace.  The 
first-grade  apatite  is  the  material  passing  off  unaffected  by  the 
magnets  of  the  Type  E  Wetherill  separators ;  the  second-grade  apa- 
tite is  the  discharge  from  the  last  three  belts  of  the  same  sep- 
arators. 

At  Lyon  Mountain  1  or  Chateaugay  Mines,  New  York,  the  ores 
carry  from  25  to  40  per  cent,  iron,  though  richer  bodies  are 
occasionally  found  which  run  from  50  to  55  per  cent,  iron;  the 
average  iron  content  of  the  ores  treated  may  be  given  as  35  per 
cent.  The  ore  consists  of  magnetite  with  orthoclase,  quartz,  and 
pyroxene;  accessory  minerals  are  titanite,  zircone  and  apatite,  all 
present  in  small  amounts.  The  magnetite  is  distributed  through 
the  mass,  and  also  occurs  in  aggregates  and  stringers.  The  mill 
flow  sheet  follows: 

The  concentrate  bins  are  of  600-ton  capacity;  there  are  two 
tailing  bins;  one  for  fine  and  one  for  coarse  material,  each  of 

1  D.  H.  Newland  and  N.  V.  Hansell,  Eng.  and  Min.  Journ.,  vol.  Ixxxii,  p.  916. 


92 


through 


ELECTRO-MAGNETIC   ORE   SEPARATION 

FLOW    SHEET   FOR  MILL   NO.   2 

Crude  ore, 
scales  and  bin 

30-in.  X  18-in.  crusher 

f-in.  screen 
oversize 


36  in.  X  6-in.  two-jaw  crusher,  225  r.p.m. 


6-mesh  screen 

through 


oversize 


36-in.  X  14-in.  rolls,  100  r.p.m. 


30-mesh 

I 


dryer 

tower  screens,  288  sq.  ft.  screening  surface 

1 6-mesh  10-mesh  6-mesh  oversize 


Ball-Norton  Ball-Norton  Wetherill  Type         Ball-Norton  36-in.  X  14-in. 

beU  separator  belt  separator  F  separator  belt  separator            rolls  100 

/\  /\  /\                        /\                      r.p.m. 

tailing  [concent.]  tailing  [concent.]  tailing  [concent.]  tailing  [concent.] 


Ball-Norton  belt  separator 

/\ 

tailing     [concent.] 

32  X  10-in.  high-speed  rolls,  300  r.p.m. 

tower  screen 
1 6-mesh  10-mesh 

Wetherill  Type  E  separator     Wetherill  Type  E  separator 


[No.  1  apatite]     [No.  2  apatite]     magnetite    [No.  1  apatite]    [No.  2  apatite]    magnetite 

I _. I 

Ball-Norton  belt  separator 

/\ 
[concent.]     [apatite  No.  2] 


THE   CONCENTRATION   OF   MAGNETITE   ORES 


FLOW  SHEET  FOR  LYON   MOUNTAIN  MILL. 
700-ton  ore  bin 


2£-inch  grizzly 


through 


oversize 
24-in.  X  30-in.  crusher 


1^-in.  grizzly 
through  oversize 

Gates'  gyratory  crusher 


I 
conveyor 

f-in.  grizzly 
through  oversize 

40-in.  X  30-in.  rolls 


elevator 

dryer 

elevator 

450-ton  bin,  two  sections 

2  trommels 
in.  to  f-in.  through 

350-ton  bin,  four  sections 


4  Ball-Norton  double-drum  separators 
[concent.]  tailing  middling 


2  sets  40  X  15-in.  rolls 
2  Ball-Norton  double-drum  separators 
[concent.]  tailing  middling  [concent.]  tailing 

Ball-Norton  double-drum  separator 


2  sets  22  X  16-in.  rolls 
2  Ball-Norton  double-drum  separators 


middling 

returned  to 

22  X  16-in.  rolls 


[concent.] 


[tailing] 


middling 

returned  to 

22  X  16-in.  rolls 


94 


ELECTRO-MAGNETIC  ORE   SEPARATION 


200  tons  capacity.  The  dryer  is  vertical  and  40  ft.  in  height; 
the  ore  drops  between  cross-laid  T-bars  coming  into  thorough  con- 
tact with  the  heated  gases.  The  furnace  is  situated  10  ft.  above 


FIG.   53.  — MINE    AND   TRESTLE   AT   LYON   MOUNTAIN. 

the  bottom  of  the  dryer,  and  the  cold  air  feeding  the  furnace 
passes  through  the  discharge  outlet  of  the  dryer,  serving  to  cool 
the  ore  and  heat  the  air  before  entering  the  fire-box.  The  tail- 


FIG.    54.  — MILL   AT  LYON   MOUNTAIN. 

ings  are  screened  in  a  J-in.  trommel,  and  after  grinding,  used  for 
locomotive  sand;  the  coarse  tailings  have  found  a  market  as  rail- 
road ballast  and  material  for  concrete  work.  Power  is  furnished 


THE  CONCENTRATION  OF  MAGNETITE  ORES 


95 


by  two  225  H.  P.  3-phase  induction  motors ;  the  actual  running  of 
the  mill  requires  250  KW.  The  capacity  of  the  mill  is  in  ex- 
cess of  50  tons  per  hour.  Sixteen  men  on  each  shift  operate  the 
mill;  of  these  four  attend  to  the  crushers  and  rolls,  three  are 
required  on  the  separators,  one  man  fires  the  dryer,  another  is 
employed  as  oiler,  one  works  in  the  motor  room,  and  there  is 
one  foreman;  the  remainder  of  the  shift  dump,  weigh,  load,  and 
sample  the  ore.  Analyses  of  the  crude  ore  and  products  follow: 


Crude  Ore, 
Per  cent. 

Concentrate 
Per  cent. 

TaUing, 
Per  cent. 

Total  iron                           

36   50 

64.72 

9.70 

Iron,  as  magnetite 

34  30 

64  53 

6.00 

Phosphorus         

0  019 

0.01 

0.028 

Titanium                  

0  089 

0.083 

0.096 

Manganese 

0  256 

0  250 

0  274 

The  average  concentrate  is  said  now  to  carry  63  per  cent,  iron 
and  0.01  per  cent,  phosphorus;  the  tailing  being  reduced  to  4 
per  cent.  iron.  The  Chateaugay  ore  commands  a  premium  for 
the  manufacture  of  low  phosphorus  iron. 

At  Port  Orem,  New  Jersey,  the  New  Jersey  Iron  Mining  Co. 
is  operating  a  magnetic-concentration  plant  on  magnetite  ores. 
The  ore  carries  magnetite  in  stringers  and  grains  in  a  gangue  of 
quartz  and  some  finely  disseminated  apatite.  It  is  crushed  in 
breakers  and  rolls  to  a  size  varying  from  20  mesh  to  J  in.,  de- 
pending upon  the  ore  treated.  A  modification  of  the  Ball-Norton 
separator  is  employed.  The  ore  carries  about  25  per  cent,  iron  and 
1  per  cent,  phosphorus;  the  concentrate  carries  61  per  cent,  iron 
and  from  0.045  to  0.3  per  cent,  phosphorus;  the  tailing  carries 
from  11  to  17  per  cent.. iron. 

At  Hibernia,  New  Jersey,  the  Joseph  Wharton  Mining  Co.  is 
operating  a  magnetic-concentrating  plant  on  magnetite  ores  which 
carry  from  38  to  40  per  cent,  iron,  0.04  per  cent,  phosphorus,  and 
no  sulphur.  The  ore  is  crushed  by  Buchanan  breakers  and  rolls  to 
\  in.,  and  is  separated  upon  a  Ball-Norton  double-drum  separator. 
One  hundred  tons  of  ore  yield  40  tons  of  concentrate,  20  tons  of 
middling,  and  40  tons  of  tailing.  The  middling  is  recrushed  in 
tight  rolls  and  repassed.  The  concentrate  carries  from  63  to  64 


96  ELECTRO-MAGNETIC  ORE  SEPARATION 

per  cent,  iron  and  0.008  per  cent,  phosphorus;  the  middling 
product  carries  40  per  cent,  iron,  and  the  tailing  from  5  to  6  per 
cent.  iron.  Dust  is  withdrawn  from  the  separator  by  a  fan,  and 
after  settling  in  a  dust  chamber,  is  sent  to  the  waste  dump. 

At  Lebanon,  Pennsylvania,  the  Pennsylvania  Steel  Co.  is 
operating  a  plant  equipped  with  Grondal  Type  V  separators.  The 
capacity  of  the  plant  is  300  long  tons  of  60  per  cent,  iron  con- 
centrate per  twelve-hour  shift,  from  a  raw  ore  carrying  40  per 
cent.  iron. 

At  Solsbury,  New  York,  the  Solsbury  Iron  Co.1  is  completing 
a  magnetic-concentration  mill  equipped  with  Ball-Norton  single- 
drum  and  Ball-Norton  belt  separators,  having  a  capacity  of  500 
tons  in  20  hours.  The  ore  is  passed  through  gyratory  crushers, 
screened,  and  the  oversize  on  1.5-in.  screens  passed  over  cobbing 
separators;  the  undersize,  reduced  to  30  mesh,  is  passed  through 
a  drying  tower  and  separated  on  the  belt-type  separators.  It  is 
expected  to  ship  a  product  carrying  69  per  cent,  iron  from  the  30- 
mesh  material  and  a  60  per  cent,  coarse-  concentrate  from  the  cob- 
bing separators. 

At  Mount  Hope,  New  Jersey,  the  Empire  Steel  &  Iron  Co.  is 
completing  a  magnetic  cobbing  plant  equipped  with  Ball-Norton 
separators  and  having  a  capacity  of  600  tons  daily. 

At  Benson  Mines,  New  York,  the  Benson  Iron  Ore  Co.  is 
building  a  magnetic-separation  mill  with  an  estimated  capacity  of 
3000  tons  daily.  Steam  shovels  are  used  to  mine  the  ore,  which 
is  crushed  in  Edison  giant  rolls  and  separated  on  Ball-Norton  sep- 
arators. 

At  Port  Henry,  New  York,  the  Cheaver  Iron  Ore  Co.  is  build- 
ing a  magnetic-concentration  mill  equipped  with  Ball-Norton  sep- 
arators. 

At  Herrang,  Sweden,2  the  Herrangs  Grufaktiebolag  is  operat- 
ing a  magnetic-concentration  and  briquetting  plant  of  50,000 
metric  tons  yearly  capacity.  The  ore  carries  about  40  per  cent, 
iron  with  1.2  per  cent,  sulphur  and  0.003  per  cent,  phosphorus. 
The  gangue  consists  partly  of  pyroxene  and  garnet.  The  ore  is 
broken  to  J  in.  in  breakers  and  ground  in  Grondal  ball  mills  to 
1  mm. 

This  mill  consists  of  a  horizontal  cylinder  built  up  of  longitud- 

1  Communicated  by  F.  R.  Switzer,  Asst.  Treas.,  Utica,  N.  Y. 

2  Communicated  by  the  Grondal-Kjellin  Company,  Ltd.,  London,  England. 


THE  CONCENTRATION  OF  MAGNETITE  ORES      97 

inal  steel  ribs,  with  cast-iron  end-plates.  Through  one  end  of  the 
cylinder  the  ore  is  introduced  with  water  over  a  roller  feeder. 
The  crushing  is  done  by  chilled  cast-iron  balls  ranging  in  size 
from  6  ins.  in  diameter  downward.  No  screens  are  required,  the 
degree  of  fineness  to  which  the  ore  is  ground  being  regulated  by 
the  speed  of  the  water  current  passing  through  the  cylinder.  The 
wear  of  the  balls  is  about  2  Ibs.  for  each  ton  of  ore  ground.  The 


FIG.   55.  — GRONDAL  SEPARATORS  AT  HERRANG. 

force  required  for  each  mill  is  from  20  to  25  H.P. :  the  capacity 
is  from  50  to  100  tons  per  24  hours,  varying  .with  the  hardness  of 
the  ore  and  the  fineness  to  which  it  is  reduced. 

The  pulp  from  the  ball  mills  is  passed  through  two  V-shaped 
settling  boxes  from  which  the  sand  is  drawn  off  through  a  pipe  at 
the  bottom ;  the  slime  remaining  in  suspension  in  the  water  is  sub- 
jected to  magnetic  treatment  by  a  pair  of  Grondal  slime  magnets. 
The  sand  and  magnetic  slime  are  treated  on  Grondal  Type  III 
and  Type  V  separators.  The  concentrate  carries  from  60  to  65  per 
cent,  iron  with  0.17  per  cent,  sulphur  and  0.0025  per  cent,  phos- 
phorus. The  tailing  product  carries  from  5  to  15  per  cent,  iron, 
and  the  waste  slime  9.6  per  cent.  iron. 

The  powdered  concentrate  is  pressed  into  briquettes  without 


98 


ELECTRO-MAGNETIC   ORE   SEPARATION 


the  use  of  binding  material,  the  moisture  in  the  concentrate  being 
regulated  to  give  a  briquette  sufficiently  firm  to  bear  handling 
from  the  press  to  the  car  used  in  the  furnaces.  The  finished  bri- 
quettes carry  63  per  cent,  iron  with  0.003  per  cent,  sulphur  and 
0.0025  per  cent,  phosphorus;  they  are  hard  but  porous,  the  per- 
centage of  porosity  being  23.9  per  cent.  Such  a  plant  as  is  de- 
scribed above  costs  in  the  neighborhood  of  $50,000  to  erect,  and 
requires  20  men,  200  H.P.  and  465  gallons  of  water  per  minute  to 


FIG.  56.  — BRIQUETTING  PLANT  AT  HERRANG. 

operate.1  It  is  probable  that  where  a  higher  scale  of  wages  ob- 
tains economical  operation  would  demand  labor-saving  appliances 
and  permit  a  reduction  in  the  working  force. 

At  Edison,  New  Jersey,2  there  is  a  large  installation  for  the 
treatment  of  magnetite  ores,  designed  by  Mr.  Thomas  A.  Edison 
and  erected  by  the  New  Jersey  and  Pennsylvania  Concentrating  Co. 
Between  the  time  of  the  design  of  this  mill  and  its  completion  a 
severe  drop  was  experienced  in  the  iron-ore  market,  due  to  the 
discovery  of  the  Mesabi  ore  beds;  the  mill  in  consequence  has 
never  been  operated  except  in  an  experimental  way.  The  mill 

1  Professor  Petersson,  E.  &  M.  J.,  May  11,  1907. 

2  Richard's  "Ore  Dressing,"  p.  1057. 


THE  CONCENTRATION   OF   MAGNETITE  ORES  99 

contains  so  many  valuable  ideas  and  is  on  such  a  large  scale  that 
it  merits  description.  The  plant  was  designed  for  4000  tons  capac- 
ity per  24  hours,  but  has  put  through  300  tons  per  hour,  which  is 
at  the  rate  of  6000  tons  per  20  hours.  The  ore  consists  of  magne- 
tite in  a  gangue  of  feldspar  with  a  little  quartz  and  apatite.  The 
ore  is  ruined  in  open  quarries  and  contains  lumps  up  to  5  tons 
in  weight.  It  is  loaded  by  steam  shovels  and  dumped  on  skips 
holding  6.5  tons  each,  which  are  hauled  to  the -mill  on -ears  by 
locomotive.  The  skips  are  of  the  open,  flat  form  used  in  quarry 
work  and  are  suspended  by  two  chains  and  hooks  at  the  front 
end  and  by  one  chain  and  hook  at  the  rear;  they  are  lifted  at  the 
mill  by  two  electric  traveling  cranes  and  then,  by  unhooking  the 
two  front  hooks,  they  are  dumped  to  (1). 

1.  One  No.  1  roller  feeder,  3  ft.  diameter  and  6  ft.  long.    To 
hopper  6  ft.  square  and  thence  to  (2). 

2.  One  pair  of  No.  1  giant  rolls,  72  ins.  X  72  ins.,  set  14  ins. 
apart.    To  (3). 

3.  One  pair  No.  2,  or  intermediate  rolls,  48  ins.  X  60  ins.,  set 
7  ins.  apart.    By  No.  1  bucket  elevator  to  (4). 

4.  One  pair  No.  3  or  first  corrugated  rolls,  36  ins.  X  36  ins., 
set  3.5  ins.  apart.     To  (5). 

5.  One  pair  No.  4  or  second  corrugated  rolls,  36  ins.  X  36  ins., 
set  1.5  ins.  apart.    To  (6). 

6.  One  pair  No.  5  or  third  corrugated  rolls,  24  ins.  X  20  ins., 
set  J  in.  apart.     By  No.  1  belt  conveyor  and  thence  by  No.  2 
bucket  elevator  to  (7). 

7.  Three  No.  1  fixed  screens  in  series,  the  upper  one  having  1J 
X  3-in.  slots  and  the  two  lower  l^-in.  X  2J-in.  slots.     Oversize, 
bolts,  roots,  etc.,  to  dump;  underside  to  (8). 

8.  One  No.  1  dryer  in  the  form  of  a  drying  kiln  with  a  dis- 
tributor at  the  top.    By  No.  2  belt  conveyor,  and  thence  by  No.  3 
bucket  elevator,  followed  by  Edison  distributing  conveyor  to  (9). 

9.  No.  1  stock  house,  holding  16,000  tons.     By  No.  4  bucket 
conveyor  to  (10). 

10.  Bin  holding  25  tons.    By  two  No.  2  corrugated  roller  feed- 
ers to  (11). 

11.  From  (10)   and  (12).     Two  sets  of  No.  6  or  three  high 
rolls,   36   ins.  X  30  ins.,   set  close  together,  but  the  feed  opens 
them  to  about  1£  ins.    Only  one  set  is  run  at  a  time.    The  crushed 
ore  is  carried  in  succession  by  two  No.  5  belt  conveyors,  one  No.  6 


100  ELECTRO-MAGNETIC  ORE   SEPARATION 

bucket  conveyor,  one  No.   5  bucket  elevator,  one  No.  7  Edison 
distributing  conveyor,  and  twenty  No.  3  roller  feeders  to  (12). 

12.  Two  hundred  and  forty  No.  2  fixed  inclined  screens  ar- 
ranged in  sixty  sets,  with  four  screens  in  series  in  each  set,  having 
•j2g.-in.  X  i-in.  slots.     Oversize  to  (11) ;  undersize  to  (13). 

13.  Sixty  No.  1  Edison  magnetic  separators.     These  are  12-in. 
magnets  and  are  arranged  in  twenty  sets,  with  three  magnets  in 
series  in  each  set.     Heads  by  two  No.  8  belt  conveyors  to  (14) ; 
tailings  by  No.  9  belt  conveyor  to  (22). 

14.  One  No.  2  dryer  in  the  form  of  a  drying  kiln  with  a  dis- 
tributor at  the  top.     To  (15). 

15.  From  (14),  (16),  and  (19).    Two  sets  No.  7  or  three-high 
rolls,  36  ins.  X  30  ins.,  set  close  together,  but  the  feed  opens  them 
to  about  J  in.    Only  one  set  is  run  at  a  time.    The  crushed  ore  is 
carried  in  succession  by  two  No.  10  belt  conveyors,  one  No.  11 
bucket  conveyor,  one  No.  6  bucket  elevator,  one  No.  12  Edison  dis- 
tributing conveyor,  and  twenty  No.  4  roller  feeders  to  (16). 

16.  Two  hundred  and  forty  fixed  inclined  screens,  No.  3,  ar- 
ranged in  sixty  sets,  with  four  screens  in  series  in  each  set,  having 
^-in.  X  £-in.  slots.     Oversize  to  (15) ;  undersize  to  (17). 

17.  Ninety-six   Edison  magnetic  separators.     They   are   8-in. 
magnets  and  are  arranged  in  thirty-two  sets,  with  three  magnets  in 
series  in  each  set.    Heads  to  (18) ;  tailings  to  (22). 

18.  Eight  dusting  chambers.     Heavy  material  to   (19);  light 
material  to  (20). 

19.  Three  hundred  and  twenty  No.  3  Edison  magnetic  separa- 
tors.    They  are  4-in.  magnets  and  are  arranged  in  sixty-four  sets 
with  five  in  series  in  each  set.    Heads  to  (21) ;  tailings  from  first 
or  upper  magnets  to  (22)  ;  tailings  from  second,  third,  fourth,  and 
fifth  magnets  to  (15). 

20.  From  (18).    One  No.  4  Edison  magnetic  separator  for  fine 
material.    Heads  to  (21) ;  tailings  are  sold  for  paint. 

21.  From  (19)  and  (20).    No.  2  and  No.  3  stock  houses  with 
a  total  capacity  of  35,000  tons.     From  these  the  concentrates  pass 
in  succession  through  the  mixers,  the  briquetting  machines  and  the 
baking  ovens. 

22.  From  (13),  (17),  and  (19),  sand  house.    Tailings  are  here 
sized  and  sold  for  mortar  sand,  etc.;  on  account  of  proximity  to 
large  cities  this  material  is  in  demand. 

The  labor  required  for  mining,  milling,  and  briquetting  is  311 


THE  CONCENTRATION   OF   MAGNETITE   ORES  101 

men  per  24  hours,  divided  into  two  shifts  of  10  hours  each,  46 
men  and  boys  mining  by  day  and  46  by  night ;  24  men  by  day  and 
24  by  night  in  the  coarse-crushing  house — to  and  including  (9)  ; 
32  men  by  day  and  32  by  night  in  the  fine-crushing  and  separating 
house;  and  66  men  by  day  and  41  by  night  doing  general  work. 

Power  is  furnished  by  steam.  A  single  Corliss  engine  of  300 
H.P.  runs  the  dynamos  for  the  magnets,  for  lighting,  and  for  the 
two  electric  cranes,  which  require  50  to  80  H.P.  each.  A  cross- 
compound  engine  of  700  H.P.  runs  the  coarse-crushing  plant.  A 
triple-expansion  vertical  engine  of  500  H.P.  runs  the  three-high 
rolls,  elevators,  conveyors  and  fans  of  the  fine-crushing  and  sep- 
arating plant. 

The  ore  contains  about  20  per  cent,  iron  and  0.7  per  cent,  to 
0.8  per  cent,  phosphorus;  the  heads  of  No.  1  magnets  (13)  contain 
40  per  cent,  iron  and  the  tailings  0.8  per  cent,  iron;  the  heads 
from  No.  2  magnets  (17)  contain  60  per  cent,  iron;  the  heads 
from  the  dusting  chambers  (18)  contain  64  per  cent,  iron;  the 
heads  from  the  No.  3  magnets  (19)  contain  from  67  to  68  per 
cent,  iron,  the  mill  tailing  carries  1.12  per  cent.  iron.  Analysis  of 
the  briquettes  show  67  to  68  per  cent,  iron,  2  to  3  per  cent,  silica, 
0.4  to  0.8  per  cent,  alumina,  0.05  to  0.10  per  cent,  manganese,  a 
trace  each  of  lime,  magnesia  and  sulphur,  0.028  to  0.033  per  cent, 
phosphorus,  0.75  per  cent,  resinous  binder,  and  no  moisture.  One 
hundred  tons  of  ore  yield  about  24  tons  of  concentrate  and  76 
tons  of  tailing.  The  tailing  from  No.  1  magnets  amounts  to  55 
per  cent,  of  the  ore  fed  to  the  mill. 

An  especially  noticeable  feature  of  the  mill  is  the  absence  of 
graded  crushing  and  sizing;  this  is  allowable  because  fine  ore  is 
not  considered  a  source  of  loss  in  the  magnetic  treatment. 

At  Guldsmedshyttan,  Sweden,  the  Guldsmedshytte  Aktiebolag 
is  operating  a  concentrating  and  briquetting  plant  of  60,000  tons 
yearly  capacity  similar  to  the  Herrang  installation  above  described. 
Grondal  No.  V  separators  are  employed. 

At  Svarto,  near  Lulea,1  a  magnetite  ore  rich  in  phosphorus  is 
being  separated  for  the  value  of  the  apatite  as  well  as  the  cleaned 
iron  concentrate.  This  plant  was  erected  in  1897  by  the  Norbot- 
tom  Ore  Improvement  Co.  to  treat  ores  from  the  Gellivara  Mines. 
The  ore  carries  from  0.01  to  3  per  cent,  phosphorus,  averaging  1 

JT.  Beckert,  Zeit.  Ver.  D.  Ing.,  vol.  xli,  p.  1307;  E.  Langguth,  "Electro- 
magnetische  Aufbereitung,"  p.  61;  E.  &  M.  J.,  vol.  Ixv,  p.  645. 


102 


ELECTRO-MAGNETIC  ORE   SEPARATION 


per  cent. ;  the  average  iron  content  is  58  per  cent.  The  texture  of 
the  ore  materially  aids  in  the  saving  of  the  apatite,  as  it  consists  of 
sharply  defined  crystals  of  the  different  minerals  whose  cohesion  is 
low. 

The  run  of  mine  ore  is  subjected  to  a  rough  hand  picking  and 
then  crushed  in  a  Blake  crusher  and  Swensen  rolls  to  pass  a  14  mm. 
screen.  The  ore  is  then,  dried  in  a  cylindrical  dryer  10  meters  long 
by  1.4  meters  diameter,  inclined  at  an  angle  of  5  degrees.  The  cyl- 


FIG.    57.  — MAGNETIC   CONCENTRATION   MILL   AT   GULDSMEDSHYTTAN. 

inder  rotates  once  in  5  seconds  and  is  heated  by  a  stream  of  hot 
gases  from  a  fire  box  at  the  lower  end.  The  ore  is  fed  to  the 
cylinder  by  revolving  feed  plates  and  at  the  discharge  falls  into 
rolls  which  reduce  it  to  pass  a  1-mm.  screen. 

The  separation  is  accomplished  by  four  Monarch  separators, 
arranged  in  two  independent  units,  two  machines  tandem.  The 
first  separator  of  each  unit  makes  a  clean  magnetite  product,  a  tail- 
ing rich  in  phosphorus,  and  a  middling  product  which  is  re-treated 
on  the  second  separator,  which  makes  two  products  only,  tailing 
rich  in  phosphorus,  and  a  concentrate.  The  dust  is  removed  from 
the  Monarch  separators  by  an  exhaust  fan  and  treated  on  a  Her- 
bele  wet-type  separator.  The  iron  product  amounts  to  85  per  cent. 


THE   CONCENTRATION   OF   MAGNETITE   ORES 


103 


of  the  feed  and  carries  70  per  cent,  iron,  and  0.127  per  cent. 
phosphorus.  The  tailing  from  the  separators  carries  25.5  per  cent, 
iron  and  13.7  per  cent,  phosphorus. 

The  tailing  is  jigged  and  the  apatite  removed  as  far  as  pos- 
sible from  the  magnetite  by  water  concentration.  The  apatite 
product  is  then  treated  chemically  for  the  removal  of  remaining 
magnetite  and  ground  to  an  impalpable  powder  in  a  ball  mill 
using  flint  grinding  balls.  The  powdered  apatite  is  mixed  with 
calcined  soda  ash  and  heated  to  a  dull-red  heat  in  a  two-stage 
calcining  furnace.  The  product  is  finely  ground,  and  as  shipped 
contains  30  per  cent,  phosphoric  acid  in  soluble  form;  it  is  used 
as  a  fertilizer.  The  mill  flow  sheet  follows  on  page  104. 


FIG.   58.  —  BRIQUETTING  FURNACE  AT  GULDSMEDSHYTTAN. 

The  capacity  of  the  plant  is  from  2000  to  2500  metric  tons  per 
week.  The  separators  take  7  amperes  at  100  volts. 

At  Grangesberg,  Sweden,  a  magnetic  concentration  plant, 
equipped  with  Eriksson,  Forsgren  and  Wenstrom  separators,  is 
treating  ores  carrying  magnetite  and  hematite  in  a  quartz  gangue. 
The  mill  flow  sheet  follows  on  page  105.1 

At  Dannemora,  Sweden,  a  magnetic  cobbing  plant  constructed 
1  Professor  Petersson,  E.  &  M.  J.,  vol.  Ixxxiii,  p.  889. 


104 


ELECTRO-MAGNETIC  ORE   SEPARATION 


FLOW  SHEET  FOR  THE   SVARTO  MILL 

Run  of  mine  ore 

! 

hand  picking 
Blake  crusher 
rolls 


14  mm.  trommel 


through 


oversize 


rolls 

_| 


I 
cylindrical  dryer 

rolls 


1  mm.  trommel 


through 


oversize- 


I 
elevator 


Monarch  separator 
apatite     middling    [magnetite] 


Monarch  separator 
apatite  [magnetite] 


I 
Monarch  separator 

apatite         middling    [magnetite] 
Monarch  separator 


apatite 


[magnetite] 


jigs  and  spitzkasten 
[magnetite  waste]  apatite 

ball  mill 

calcining  furnace 
[soluble  phosphate] 

in  1903  is  in  operation  on  small  ores;  the  Wenstrom  separator  is 
employed.  The  run  of  mine  ore  is  subjected  to  hand  picking,  a 
clean  magnetite  product  carrying  up  to  60  per  cent,  being  thrown 
out  and  sent  directly  to  the  furnaces.  The  ore  is  lifted  by  ele- 
vator to  the  top  floor  of  the  mill  and  dumped  into  a  bin  of  1.5 
cu.  yds.  capacity.  The  mill  flow  sheet  follows  on  page  106. 1 

'  Professor  Petersson,  E.  &  M.J.,  vol.  Ixxxiii,  p.  890. 


THE  CONCENTRATION   OF   MAGNETITE  ORES 


105 


FLOW  SHEET  FOR  THE  GRANGESBERG  MILL 
Railroad  car 


grizzly  with  3-in.  openings 


through 
Ferraris  oscillating  screen  with 


3  to 


ns. 


and  %-in.  holes 
U  to  *XK  in. 


Wenstrom  cobbing  separator 

nonmagnetic  [magnetite] 
I — picking  belt— j 

[hematite]  [tailing] 


oversize 

hand  picked 
through  %  in. 
Eriksson  separator 
tailing         [magnetite] 


[hematite]         [tailing] 


Wenstrom  cobbing  separator 
[magnetite]     nonmagnetic 


Forsgren  separator 
nonmagnetic    [magnetite] 


2  jigs 
[hematite]    [tailing] 


I 
Ferraris  screens  with  f-in.  and  f-in.  holes 

f  to  %  in. 

I 
1  jig 

[hematite]    [tailing] 


|  to  |  in. 

I 
8  jigs 

[hematite]    [tailing] 


The  crude  ore  carries  magnetite,  hematite,  and  pyrites  in  peg- 
matite and  schistose  material.  The  ore  carries  about  40  per  cent, 
iron  and  the  concentrate  from  60  to  61  per  cent.  iron.  The  con- 
centrate is  roasted  to  remove  sulphur. 

At  Flogbeget,1  near  Ludvika,  Sweden,  magnetic  concentration 
plant  built  in  1906  and  employing  the  Grondal  Type  V  separator 
is  in  operation  on  magnetic  ores. 

At  Klacka,  Sweden,  the  Klacka-Lerbergs  Grufvebolag  is  oper- 
ating a  magnetic  concentration  plant  equipped  with  Wenstrom 
cobbing  separators  for  the  sizes  coarser  than  f  in.  and  the  Grondal 
Types  I  and  II  for  the  fine  sizes. 

After  passing  the  ball  mills  77  per  cent,  of  the  pulp  passes  0.15 
mm.  The  ore  carries  from  38  to  39  per  cent,  iron,  and  the  con- 
centrate, amounting  to  45.9  per  cent,  of  the  feed,  58  to  59  per 

1  Professor  Petersson,  E.  &  M.  J.,  vol.  Ixxxiii,  p.  889. 


106 


ELECTRO-MAGNETIC  ORE   SEPARATION 


So 


THE   CONCENTRATION   OF   MAGNETITE   ORES  107 

FLOW  SHEET  FOR  THE  FLOGBEGET  MILL 
Crude  ore 

Blake  crusher  19X24  ins. 

| 
130-ton  bin 

feed  rolls 

conveyor  belt 

2  Grondal  ball  mills  crushing  to  0.8  mm. 

Grondal  Type  V  separator 
[tailing] middling 

Grondal  Type  V  separator 
[tailing] —       first  concentrate 

tube  mill,  grinding  to  0 . 2  mm. 
bucket  elevator 

Grondal  Type  V  separator 
[tailing] -  second  concentrate 

Grondal  Type  V  separator 
[tailing] [final  concentrate] 

water  separator 
briquetting  plant 

cent.  iron.  The  tailing  product  carries  from  12.7  to  14.6  per  cent. 
iron.1  The  plant  is  operated  by  6  men,  and  requires  20  H.P.  and 
200  liters  of  water  per  minute.  The  mill  produces  20  metric  tons 
of  concentrate  per  day. 

At  Persberg,  Sweden?  a  Grondal  Type  I  separator  is  treating 
low-grade  magnetite  ore  carrying  from  15  to  20  per  cent.  iron.  The 
ore  is  crushed  in  a  ball  mill  to  pass  5  mm.  The  finished  product 
carries  57  per  cent,  iron  and  amounts  to  21  per  cent,  of  the  feed. 
The  capacity  of  the  plant  is  2500  metric  tons  per  annum.  Eight 
men  are  employed  and  55  H.P.  are  required  to  operate  the  plant. 
The  water  consumption  is  200  liters  per  minute.  The  separator  is 
excited  by  from  5  to  7  amperes  at  30  volts. 

At  Romme,  Sweden,  a  lean  magnetite  ore  carrying  22  to  25  per 
cent,  iron  is  separated  by  Grondal  Type  II  separators.  The  ore  is 
crushed  in  a  ball  mill  to  pass  1.5  mm.  The  finished  product  car- 
ries from  60  to  64  per  cent,  iron  and  the  tailing  averages  10.6  per 

1  Dr.  Weiskopf,  "Stahl  und  Eisen,"  vol.  xxv,  p.  532. 


108  ELECTRO-MAGNETIC   ORE   SEPARATION 

FLOW  SHEET  FOR  THE  KLACKA  MILL 

Crude  ore 

Blake  crusher  to  If  ins. 

conical  revolving  screen,  1  f-ins.  and  |-in.  holes 
oversize  If  to  f  ins.  through  f  in. 

Wenstrom  cobbing  separator     Wenstrom  cobbing  separator 

[magnetite]   [tailing]   middling  [magnetite]  [tailing]   middling 

I I 


2  Grondal  ball  mills 

Ferraris  shaking  screen,  IJ-mm.  holes 
oversize  through  \  mm. 

Grondal  Type  II  separator  Grondal  Type  I  separator 

[magnetite]         [tailing]  [magnetite]     middling 

Grondal  Type  II  separator 
[magnetite]     [tailing] 

cent.  iron.  Each  separator  puts  through  \  metric  ton  per  hour ; 
the  magnets  are  excited  by  3  amperes  at  90  volts.  Fourteen  men 
and  60  H.P.  are  required  to  operate  the  plant.  The  water  used 
amounts  to  600  liters  per  minute.1 

At  Strassa,  Sweden,  Grondal  Type  I  and  Type  II  separators 
are  treating  ore  carrying  36.8  per  cent,  iron,  0.014  per  cent,  phos- 
phorus, and  0.11  per  cent,  sulphur.  The  ore  is  crushed  to  pass 
1  mm.  in  ball  mills.  The  finished  product  carries  61.58  per  cent, 
iron,  0.006  per  cent,  phosphorus,  and  0.045  per  cent,  sulphur;  it 
amounts  to  45.5  per  cent,  of  the  raw  ore.  The  tailing  carries  12 
per  cent.  iron.  The  mill  has  a  capacity  of  from  30  to  40  metric 
tons  daily  and  employs  17  men.  From  30  to  35  H.P.  are  required 
to  operate  the  plant,  and  from  150  to  200  liters  of  water  are  used 
per  minute.  The  separator  is  excited  by  1.7  amperes  at  30  volts.1 
A  Grondal  Type  V  separator  and  a  briquetting  plant  has  been 
added  to  this  installation. 

At  Bredsjo,  Sweden,  a  Grondal  Type  II  separator  is  treating  a 
magnetite  ore  carrying  45.3  per  cent,  iron,  0.0083  per  cent,  phos- 
phorus, and  0.198  per  cent,  sulphur.  The  ore  is  crushed  to  pass 

i  Dr.  Weiskopf,  "Stahl  und  Eisen,"  vol.  xxv,  p.  532. 


THE   CONCENTRATION   OF   MAGNETITE   ORES  109 

1.5  mm.  The  finished  product  amounts  to  48.6  per  cent,  of  the 
feed  and  carries  64  per  cent,  iron,  0.0023  per  cent,  phosphorus, 
and  0.082  per  cent,  sulphur.  The  tailing  carries  7  per  cent.  iron. 
40  H.P.  are  required  to  operate  the  plant,  which  employs  4  men 
and  has  a  capacity  of  30  metric  tons  per  day.1  A  Grondal  Type  V 
separator  has  recently  been  added  to  this  plant.  The  concentrate 
is  briquetted.  The  present  capacity  of  the  plant  is  40,000  metric 
tons  per  annum. 

At  Norberg,  Sweden,  an  Ericksson  separator  is  used  at  the  Kall- 
mora  Separating  Works,  treating  magnetite  ores. 

At  Bagga,  Sweden,  a  Grondal  Type  I  separator  is  working  on 
an  ore  carrying  magnetite,  hematite,  amphibole  and  quartz.  It 
averages  from  30  to  40  per  cent.  iron.  The  finished  product 
amounts  to  63.7  per  cent,  of  the  raw  ore  and  carries  from  60  to 
62  per  cent.  iron.  Ball  mills  are  used  for  fine  grinding.  The  mag- 
nets are  excited  by  from  8  to  10  amperes  at  35  volts.1 

At  Lomberget,  Sweden,  a  magnetic-concentration  mill  employ- 
ing the  Forsgren  separator  has  been  in  operation  on  magnetite  ores 
since  1903. 

At  Bjornberget,  Sweden,  a  magnetic-concentration  mill  em- 
ploying the  Eriksson  separator  has  been  in  operation  on  magne- 
tite ores'  since  1904. 

At  Kungsgrufvan,  Sweden,  a  magnetic-concentration  mill  em- 
ploying the  Froeding  separator  has  been  in  operation  on  magnetite 
ores  since  1905. 

At  Langgrufvan,  Sweden,  a  magnetic-concentration  mill  em- 
ploying the  Froeding  separator  has  been  in  operation  on  magnetite 
ores  since  1905.  A  Morgardshammer  separator  has  recently  been 
added  to  this  plant. 

At  Vintjarn,  Sweden,  a  magnetic-concentration  mill  erected  in 
1906  is  in  operation  on  magnetite  ores  employing  the  Hallberg 
separator. 

At  Hjulsjo,  Sweden,  a  magnetic-concentration  mill  erected  in 
1906  is  in  operation  on  magnetite  ores.  The  Grondal  Type  V 
separator  is  employed.  The  concentrate  is  briquetted. 

At  Lulea,  Sweden,  the  Karlsvik  Mill,  built  in  1906,  is  treat- 
ing magnetite  ores  on  Grondal  Types  IV  and  V  separators.  The 
concentrate  is  briquetted.  The  crude  ore  carries  1  per  cent,  phos- 
phorus, which  is  reduced  to  0.005  per  cent,  in  the  concentrate. 

*  Dr.  Weiskopf,  "Stahl  und  Eisen,"  vol.  xxv,  p.  532. 


110 


ELECTRO-MAGNETIC   ORE   SEPARATION 


At  Uttersberg,  Sweden,  the  Uttersberg  Bruks  Aktiebolag  is 
operating  a  magnetic-concentration  mill  on  magnetite  ores.  The 
plant  was  built  in  1906  and  has  a  yearly  capacity  of  12,000  metric 
tons.  The  Grondal  Type  V  separator  is  employed.  The  con- 
centrate is  briquetted. 

At  8yd  Varanger,  Norway?  a  magnetic-separation  plant  hav- 
ing a  yearly  capacity  of  1,200,000  tons  of  crude  ore  is  being  in- 
stalled. It  will  contain  56  Grondal  ball  mills,  200  Grondal  N"o.  5 
separators,  and  20  Grondal  briquetting  kilns.  The  ore  will  be 
mined  by  steam  shovels.  The  test  runs  on  this  ore  give  the  follow- 
ing results : 


Per  cent. 
Iron 

Per  cent. 
Sulphur 

Per  cent. 
Phosphorus 

•Crude  ore  

38.0 

0.066 

0.030 

Ooncentrate  

68.3 

0.026 

0.014 

Tailing.                          

5  5 

Briquette 

68  0 

0  006 

0  014 

It  is  expected  to  produce  600,000  tons  of  briquettes  yearly, 
which  will  be  shipped  to  Germany. 

At  Salangen,  Norway,  a  Grondal  concentrating  and  briquetting 
plant  having  a  yearly  capacity  of  300,000  tons  of  ore  is  being  in- 
stalled. The  test  runs  on  this  ore  give  the  following  results : 


Per  cent. 
Iron 

Per  cent. 
Sulphur 

Per  cent. 
Phosphorus 

Orude  ore                   

35  7 

0  039 

0.23 

Concentrate 

69  3 

0  019 

0  009 

Tailing          

4  9 

It  is  expected  to  produce  100,000  tons  of  briquettes  yearly, 
which  will  be  shipped  to  Germany. 

At  Langbau  Eisberg,  Kantorp,  and  Striberg,  Sweden?  the  fol- 
lowing type  of  mill  is  used  for  the  separation  of  magnetite  and 
hematite  from  waste: 


1  Jour.  Can.  Mining  Inst.,  vol.  xi,  p.  153.     P.  McN.  Bennie. 

2  Dr.  Weiskopf,  "Stahl  und  Eisen,"  vol.  xxv,  p.  532. 


THE   CONCENTRATION   OF   MAGNETITE   ORES  111 

Feed 

Gates  crusher 
ball  mill  with  1-mm.  screen 
Grondal  separators,  Types  I  and  II 
[magnetite]  nonmagnetic 

jigs 
[hematite]  [waste] 

At  Pitlcaranta,  Finland,  a  plant  equipped  with  Dellvik-Grondal 
separators  has  been  in  operation  since  1894,  treating  a  low-grade 
magnetite  ore.  The  ore  carries  magnetite  in  tough  serpentine  ac- 
companied by  small  amounts  of  blende,  pyrite,  chalcopyrite,  and 
pyrrhotite.  The  ore,  which  is  intimately  mixed,  is  crushed  with 
difficulty;  the  average  size  of  grain  is  somewhat  less  than  J  mm. 
The  ore  carries  on  an  average  30  per  cent,  iron,  of  which  80  per 
cent,  only  is  in  the  form  of  magnetite,  the  balance  being  chemic- 
ally combined  as  sulphides  and  silicates;  it  carries  from  4  to  5 
per  cent,  sulphur.  The  first  mill  was  built  in  1894  and  was  en- 
larged to  350  metric  tons  daily  capacity  in  1898;  it  is  situated  at 
Ladogasse  3.5  to  7  km.  from  the  mines,  with  which  it  is  connected 
by  rail. 

The  tracks  from  the  mines  deliver  ore  into  bins  10  meters 
above  the  sill  floor  of  the  mill,  from  which  the  crushers  are  fed 
direct.  There  are  four  rock  breakers  which  handle  ore  up  to  250 
mm.  size.  From  the  breakers  the  ore  is  delivered  in  egg  size  to 
eight  Grondal  ball  mills.  The  ball  mills  are  cast-iron  cylinders 
lined  with  armor  plate ;  there  are  two  sizes  employed.  Four  of  the 
mills  are  1.75  meters  in  diameter  by  0.8  meter  long,  and  four  are 
2  meters  diameter  by  1  meter  long.  The  cylinders  are  turned  on 
an  inclined  axis,  the  crushing  being  accomplished  by  cast-steel 
balls.  The  smaller  mills  are  employed  on  the  more  easily  crushed 
ores  and  put  through  from  8  to  50  tons  in  24  hours;  the  larger 
mills  were  designed  especially  for  the  hardest  ore  and  treat  30 
tons  per  24  hours.  The  linings  are  renewed  once  in  15  months, 
and  fresh  balls  are  introduced  from  time  to  time.  The  ore  is 
crushed  to  pass  1  mm.,  but  a  large  percentage  is  much  finer;  a 
screen  analysis  of  the  discharge  of  ball  mills  follows: 


112  ELECTRO-MAGNETIC  ORE   SEPARATION 


Size  in  millimeters 

Per  cent, 
of  Total 

Over  1  mm          .    .    .    

1    7 

1  0    toO  5                                                                        .... 

1    2 

0  5    to  0  33  

3.8 

0  33  to  0  25          

7.5 

0  25  to  0  16                    

22  4 

0  16  to  0  125 

19  6 

Through  0  125                

43.8 

100.0 

Tests  on  the  discharge  of  the  mills  show  but  44  per  cent,  of 
the  magnetite  to  exist  as  free  particles,  and  as  a  result  the  con- 
centrate rarely  exceeds  61  per  cent,  iron;  a  higher-grade  concen- 
trate could  be  made,  but  it  would  be  at  the  expense  of  such  a  loss 
in  the  tailing  as  to  eliminate  profit  on  this  low-grade  ore.  The 
products  from  the  old  mill  carried  from  65  to  71  per  cent,  iron  in 
the  concentrate  and  1  to  1£  per  cent,  iron  present  as  magnetite  in 
the  tailing;  the  new  mill  concentrate  carries  from  59  to  61  per  cent, 
iron,  and  the  tailing  from  J  to  1  per  cent,  iron  present  as  mag- 
netite. The  raw  ore  contains  from  0.08  to  1  per  cent,  phosphorus; 
the  concentrates  average  0.042  per  cent,  phosphorus;  the  sulphur 
in  the  concentrate  is  0.6  per  cent.,  mostly  as  blende,  which  mineral 
is  intimately  associated  with  the  magnetite. 

The  separators  take  8  amperes  at  35  volts  and  put  through 
from  25  to  50  tons  of  ore  per  day,  according  to  the  iron  content. 
The  ball  mills  deliver  by  gravity  to  the  separators  which  are  2 
meters  above  the  working  floor  and  5  meters  above  the  highest 
waste  discharge. 

The  fine  concentrate  is  allowed  to  drain  for  a  few  days  and  is 
then  pressed  into  briquettes  which  are  sintered  into  a  firm  mass 
by  exposure  to  a  heat  of  800°  C.,  which  also  largely  eliminates  the 
sulphur. 

In  1900  425-kgm.  of  61  per  cent,  concentrate  were  made  from 
one  ton  of  raw  ore.  One  metric  ton  of  61  per  cent,  concentrate 
cost  $3.40  during  the  same  period. 

Power  is  derived  from  a  waterfall  7  km.  from  the  mill  and 
transmitted  by  electricity:  the  ball  mills,  crushers,  and  separators 
take  160  E.H.P.  and  the  elevator,  pumps,  and  railroad  respectively 


THE  CONCENTRATION  OF   MAGNETITE   ORES 


113 


8,  6,  and  25  E.H.P. 
8°  C.1 


In  winter  the  feed  water  is  warmed  to  7  or 


SEPARATION-   OF   MAGNETITE   AS   AN    IMPURITY 

Certain  ores  of  zinc  and  lead,  corundum,  etc.,  carry  magnetite 
where  this  mineral  is  regarded  as  an  objectionable  impurity  and 
from  which  it  is  eliminated  by  magnetic  separation. 

At  Santa  Olalla,  Huelva,  Spain,2  the  Sociedad  Minas  de  Cala 
is  operating  a  magnetic  separating  plant  on  magnetite  ores  carry- 
ing chalcopyrite,  and  also  experimenting  on  a  mixture  carrying 
the  same  minerals  with  hematite  and  silica. 

The  ore  is  reduced  by  jaw  crusher  to  3  to  5  cm.  and  delivered 
by  bucket  elevator  to  hopper  bins  having  capacity  for  10  hours'  run. 
From  these  bins  the  ore  is  fed  to  a  Smidt  ball  mill  by  an  Eriks- 
son automatic  feeder,  and  reduced  to  pass  1  mm.  This  pulp  is 
sent  by  launder  to  an  Eriksson  magnetic  separator.  The  results 
of  the  separation  follow: 

SEPARATION   OF  MAGNETITE  AND   QUARTZ 


Fe 
Per  Cent. 

SiO, 
Per  Cent. 

Feed 

39  33 

26  86 

Concentrate  (1  mm.)  

55  20 

15  06 

Concentrate  (^  mm  )                                  .... 

61  02 

9  26 

Waste  

6  21 

54  50 

SEPARATION   OF  CHALCOPYRITE  FROM  MAGNETITE 


Fe 
Per  Cent. 

Cu 
Per  Cent. 

Feed  

61  55 

0  27 

Magnetic  product  

65  47 

0  06 

Nonmagnetic  product. 

50  00 

1   18 

1  Gustav  Grondal,  "Oest.  Zeit.  B.-,  H.-  und  S.-Wesen,"  vol.  xlix,  p.  429; 
Edouard  Primosigh,  ibid.,  vol.  xlvii,  p.  51;  "Revista  Minera,"  vol.  liii,  p.  109. 

2  Communicated  by  Don  Mariano  Auguatin,  Ingeniero  de  Minas,  Santa 
Olalla,  Spain. 


114  ELECTRO-MAGNETIC  ORE  SEPARATION 

The  reseparation  of  the  magnetite  concentrates  is  made  to 
remove  the  copper  with  its  combined  sulphur;  what  disposal  is 
made  of  this  iron-copper-sulphur  product  could  not  be  learned. 

At  the  Ryttshytans  Zinc  Mines,  Sweden,  a  Grondal  Type  I 
separator  1  is  employed  to  separate  magnetite  from  blende. 

In  Raglan  Township,  Ontario,  the  Canada  Corundum  Co.2 
employs  a  magnetic  separator  in  cleaning  corundum  concentrates. 
The  ore  carries  corundum  associated  with  magnetite  and  mica  in  a 
feldspathic  gangue.  The  ore  is  crushed  with  breaker  and  rolls  and 
concentrated  with  jigs  and  tables.  The  concentrates  passing  8 
mesh  are  dried  and  the  magnetite  removed  by  the  separator.  The 
output  is  about  three  tons  of  cleaned  concentrates  per  day. 

1  Dr.  Weiskopf,  "Stahl  und  Eisen,"  vol.  xxv,  p.  532. 

2  Richards,  "Ore  Dressing,"  p.  1078. 


VI 
THE    SEPARATION    OF    PYRITE    AND   BLENDE 

THE  co-occurrence  of  the  sulphides  of  zinc  and  iron  is  fre- 
quent; blende  and  pyrite,  or  marcasite,  are  found  together  in  im- 
portant ore  bodies  which  are  worked  for  the  value  of  the  contained 
zinc,  and  many  lead  deposits  in  their  lower  horizons  carry  zinc  and 
iron  sulphides.  Galena  may  be  separated  in  the  wet  way  from 
both  of  the  lighter  sulphides,  but  the  specific  gravities  of  the  lat- 
ter are  too  similar  to  permit  their  separation  from  each  other  by 
any  method  depending  upon  specific  gravity. 

The  presence  of  iron  in  zinc  ores  is  very  undesirable  for  metal- 
lurgical reasons  connected  with  the  reduction  of  zinc,  and  this, 
fact,  together  with  the  similar  specific  gravities  of  the  sulphides  of 
these  metals,  gives  rise  to  one  of  the  most  important  fields  of  mag- 
netic separation. 

The  middling  products  from  mills  treating  galena-blende-py- 
rite  ores  frequently  carry  an  important  value  in  gold  and  silver 
locked  up  in  the  pyrite.  The  presence  of  any  considerable  amount 
of  zinc  in  such  middling  renders  it  unsalable  at  the  lead  smelters, 
or  involves  the  payment  of  a  heavy  penalty  for  each  unit  of  zine 
above  a  certain  standard,  usually  10  per  cent.,  and  their  iron  con- 
tent renders  them  unsalable  at  the  zinc  smelters.  If,  however, 
the  pyrite  and  blende  are  separated,  two  valuable  products  result. 

Pyrite  (FeS2,  sp.  gr.  4.8  to  5.2)  is  almost  nonmagnetic ;  in  some 
specimens  it  has  been  reported  as  diamagnetic,  and  in  others  as 
possessing  a  feeble  paramagnetism ;  it  is  not  attracted  by  the  fields 
of  the  most  powerful  separators.  On  roasting  it  is  readily  trans- 
formed into  the  magnetic  sulphide,  and  on  the  continuation  of  the 
roast,  into  a  strongly  magnetic  oxide  analogous  to  the  mineral 
magnetite.  Pyrite,  in  some  specimens,  on  being  heated  at  a  quite 
low  temperature  for  a  minute  or  two,  develops  an  iridescent  film  of 
magnetic  sulphide,  which  imparts  sufficient  permeability  to  cause 
it  to  be  attracted  by  fields  of  low  intensity.  The  varying  magnetic 

115 


116  ELECTRO-MAGNETIC   ORE   SEPARATION 

behavior  of  pyrite  may  be  in  some  way  connected  with  its  several 
crystalline  forms. 

Marcasite  (FeS2  sp.  gr.  4.6  to  4.85)  is  similar  to  pyrite  in 
its  magnetic  qualities. 

Sphalerite  or  blende  (ZnS,  sp.  gr.  3.9  to  4.2)  varies  in  per- 
meability according  to  the  percentage  of  isomorphic  iron  and  man- 
ganese sulphides  contained  by  it.  The  pure  sulphide  of  zinc,  as 
represented  in  the  light-straw  colored  varieties,  is  diamagnetic, 
while  the  highly  ferriferous  variety,  called  marmatite  and  "black 
jack/'  in  which  the  combined  iron  may  reach  12  or  14  per  cent., 
may  be  even  ferromagnetic.  Pure  blende,  or  "  rosin  jack,"  carries 
67  per  cent,  zinc,  while  "marmatite"  rarely  carries  over  51  or 
52  per  cent.  zinc.  Blende  carrying  as  low  as  J  per  cent,  iso- 
morphous  iron  becomes  appreciably  magnetic  upon  roasting. 
Blende  is  being  separated  as  a  magnetic  product  at  several  mills  in 
Colorado,  in  Europe  and  in  Australia.  The  degree  of  magnetism 
appears  to  depend  upon  the  ratio  of  the  two  sulphides  contained, 
which  varies  from  3  parts  ZnS  to  1  of  FeS2,  to  5  parts  ZnS  to  1 
of  FeS2,  and  in  any  given  ore  the  individual  crystals  of  sphalerite 
may  vary  from  the  nonmagnetic  straw-colored  blende  to  strongly 
magnetic  marmatite.  A  dark  color  is  not  necessarily  indicative  of 
high  iron  content. 


SEPARATION"  OF  ROASTED  PYRITE  AND  MARCASITE  FROM 
NONMAGNETIC    BLENDE 

As  neither  pyrite  nor  marcasite  possesses  sufficient  permeability 
to  be  attracted  by  even  the  most  intense  magnetic  fields,  a  pre- 
liminary roast  is  necessary  before  they  may  be  separated  from 
the  blende.  There  are  two  methods  for  rendering  iron  sulphide 
magnetic:  a  slight  roast  with  the  formation  of  the  magnetic  sul- 
phide, or  a  more  complete  roast  with  the  formation  of  a  magnetic 
oxide  of  iron. 

The  magnetic  compounds  of  iron  formed  by  roasting  the  sul- 
phide are  strongly  magnetic  and  are  attracted  by  fields  of  low 
intensity,  but,  as  the  quality  of  the  separation  made  depends  en- 
tirely upon  the  uniform  magnetic  quality  of  the  material  pre- 
sented to  the  separators,  the  roasting  is  the  most  important  step  in 
the  whole  process.  Almost  any  separator  can  make  clean  products 


THE  SEPARATION  OF   PYRITE  AND  BLENDE  117 

when  fed  with  properly  roasted  material,  but  no  separator  can  do 
satisfactory  work  upon  a  poorly  roasted  feed. 

Upon  roasting  pyrite  or  marcasite  with  access  of  air  a  portion 
of  the  sulphur  is  driven  off  as  S02  and  the  nonmagnetic  FeS2 
(pyrite)  is  transformed,  superficially  at  least,  to  Fe7S8  (analogous 
to  pyrrhotite)  which  is  strongly  magnetic.  This  operation  is  a 
difficult  one  to  control  in  most  furnaces,  however,  as  it  is  easy  to 
oxidize  some  of  the  iroc,  making  a  product  of  uneven  permeability. 

If  the  sulphur  is  completely  driven  off  by  the  roast  Fe304  re- 
sults, which  is  strongly  magnetic.  Should  the  roast  be  carried 
farther,  another  atom  of  oxygen  is  taken  up  by  the  iron  and  Fe203 
results,  which  is  quite  feebly  magnetic,  being  analogous  to  the  min- 
eral hematite.  These  two  oxides  of  iron  pass  from  one  to  the 
other,  according  as  the  atmosphere  of  the  furnace  is  reducing  or 
oxidizing.  The  artificial  magnetite,  the  black  oxide  produced  by 
the  roast,  loses  its  magnetism  more  readily  than  the  natural  mag- 
netite, and  is  converted  into  the  feebly  magnetic  red  oxide.  This 
may  in  turn  be  converted  back  to  the  black  oxide  by  exposing  it 
to  a  reducing  atmosphere  at  the  end  of  the  roast. 

Pyrite  and  marcasite  begin  to  loose  their  sulphur  and  change 
over  into  the  magnetic  sulphide,  and  finally  into  the  oxides,  at 
a  temperature  of  370°  C.,  and  the  roast  must  be  conducted  between 
this  point  and  the  ignition  point  of  blende,  which  is  about  600°  C. 
Below  400  to  460  degrees  the  pyrite  does  not  become  thoroughly 
magnetic  and  the  usual  temperature  employed  is  just  below  the 
ignition  point  of  blende.  If  this  temperature  be  slightly  exceeded 
the  only  result  is  a  superficial  oxidation  of  the  blende ;  a  tempera- 
ture of  620  degrees  was  attained  without  harmful  results  in  some 
experiments  carried  out  by  Messrs.  Hofman  and  Norton.1  Should 
this  heat  be  maintained,  however,  a  serious  loss  would  result 
through  the  oxidation  of  the  fine  particles  of  blende. 

In  plants  where  the  quantity  of  material  treated  is  sufficient 
to  make  it  feasible,  the  ore,  or  concentrate,  should  be  sized  ber 
fore-  roasting.  Eoasting  and  magnetization  take  place  from  the 
surface  inward,  and  in  a  mass  of  ore  composed  of  coarse  and 
fine  particles  the  finer  sizes  will  have  been  overroasted  before 
the  lumps  have  been  affected  to  their  centers.  If  a  medium  roast 
is  given  the  mixture  the  larger  lumps  will  have  centers  of  un- 
changed pyrite,  while  the  fine  particles  may  have  been  converted 

»  Trans.  A.I.M.  E.,  September,  1904. 


118  ELECTRO-MAGNETIC  ORE  SEPARATION 

into  the  nonmagnetic  sesquioxide,  and  it  is  evident  that  a  clean 
separation  of  such  a  product  is  out  of  the  question.  If  a  quick, 
light  roast  is  carried  out  with  a  view  to  the  formation  of  a  film  of 
magnetic  sulphide  on  the  surfaces  of  the  particles,  a  fairly  uni- 
form product  may  result  from  the  treatment  of  unsized  material; 
the  same  is  true  when  the  roast  is  carried  to  the  complete  forma- 
tion of  the  magnetic  oxide  in  a  reducing  atmosphere.  With  large 
lump  ore  it  is  difficult  to  tell  when  the  roast  has  penetrated  to  the 
centers  of  the  lumps,  and  the  process  requires  too  much  time. 
With  very  fine  material  the  interstitial  spaces  are  small,  and,  the 
material  having  a  tendency  to  pack,  the  reducing  gases  reach  all 
the  particles  with  difficulty;  also,  very  fine  particles  of  blende  may 
be  converted  into  the  oxide  of  zinc  and  pass  out  of  the  furnace  with 
the  gases,  and  dust  chambers  must  be  provided  to  save  as  much  of 
this  material  as  possible.  While  it  may  not  be  definitely  stated, 
certain  experimenters  have  given  8  mesh  as  the  best  size  for  blende- 
pyrite  concentrate  for  good  results  in  roasting. 

If  the  roast  be  conducted  with  too  free  an  access  of  air,  the 
particles  will  be  made  up  of  concentric  rings  of  different  mag- 
netic permeability,  the  surface  will  consist  of  a  layer  of  nonmag- 
netic sesquioxide  beneath  which  will  be  found  a  layer  of  black 
magnetic  oxide,  enclosing,  perhaps,  a  core  of  unchanged  sulphide, 
the  division  between  the  two  being  marked  by  a  layer  of  the  mag- 
netic sulphide.  Unless  the  roast  has  been  carried  too  far  the  mag- 
netic oxide  will  impart  sufficient  permeability  to  the  whole  particle 
to  cause  it  to  be  taken  up  by  the  magnet,  unless  decrepitation 
breaks  these  layers  apart,  in  which  case  each  behaves  according  to 
its  individual  permeability,  and  nonmagnetic  iron  finds  its  way 
into  the  blende  concentrate.  Separation  should  be  carried  out  upon 
ore  as  it  comes  from  the  furnace,  cooled  in  such  a  manner  as  not 
to  induce  decrepitation,  and  no  part  of  the  separator  feed  should 
be  crushed  after  roasting.  Particles  which  have  been  fritted  to- 
gether should  be  recrushed,  but  also  reroasted  before  separation. 

Much  of  the  concentrate  roasted  ranges  in  size  from  T\  to  J 
in.,  but  after  roasting,  all  but  a  small  percentage  of  the  iron  in 
this  concentrate  will  pass  a  20-mesh  screen.  This  is  due  to  the 
breaking  up  of  the  particles  under  the  influence  of  the  roast.  If 
a  partially  roasted  particle  of  iron  sulphide  is  broken,  a  network  of 
fine  black  lines  of  the  oxide  will  be  seen,  reaching  perhaps  the 
center  of  the  particle,  the  spaces  between  them  being  composed 


THE  SEPARATION  OF   PYRITE  AND  BLENDE  119 

of  unchanged  sulphide.  This  seems  to  indicate  that  the  roast  pro- 
ceeds more  rapidly  along  the  boundaries  of  the  crystals  (forming 
an  aggregate  of  the  mineral)  than  through  the  individual  crystals, 
causing  these  aggregates  to  split  up.  The  tendency  of  pyrite  and 
marcasite  to  decrepitate  at  a  lower  temperature  than  blende  has 
been  employed  to  separate  these  minerals,  screening  following  the 
roast.  , 

There  are  many  types  of  roasting  furnaces  on  the  market 
which,  with  proper  management,  may  be  made  to  do  efficient  work. 
The  principal  requirement  is  that  the  admission  of  air  shall  be 
under  complete  control.  Several  forms  of  mechanical  furnaces  are 
in  extensive  use,  and  the  old  shaft  furnaces  may  be  made  to  do 
good  work ;  for  the  finer  sizes,  hearth  furnaces  do  good  work.  The 
time  required  for  a  good  roast  may  be  said  to  vary  from  -J  hour  to  2 
hours  for  fine  concentrate,  up  to  3  or  3£  hours  for  coarse  material, 
roasting  for  the  magnetic  oxide.  The  roasted  pyrite  or  marcasite 
should  be  dark-brown  in  color,  almost  black;  a  decided  reddish 
tinge  indicates  overroasting.  The  magnetic  sulphide  is  black,  and 
requires  little  time  for  its  formation. 

If  there  is  tendency  toward  overroasting,  the  air  inlets  should 
be  sealed  up,  and  all  entering  the  furnace  should  be  made  to  pass 
through  the  fire  box,  where  such  is  used.  The  addition  of  a  little 
coke  or  hard  coal  may  be  resorted  to  at  the  end  of  the  roast  to  re- 
convert to  the  black  oxide  any  nonmagnetic  red  oxide  which  may 
have  been  formed.  Subjecting  the  roasting  ore  to  the  action  of  re- 
ducing gases  is  successfully  employed  in  Europe  for  this  purpose. 

It  is  probable  that  in  many  American  plants  whose  output  is 
not  sufficient  to  warrant  the  installation  of  the  more  expensive 
types  of  furnace  a  small  hearth  would  be  advantageous  for  the 
re-treatment  of  the  middling  product  from  the  separators. 

The  roast  may  be  considered  satisfactory  when  the  separators 
make  a  recovery  of  from  85  to  90  per  cent,  of  the  total  zinc  in  the 
raw  concentrate,  and  yield  a  clean  blende  product  carrying  1.5  to 
2.5  per  cent,  iron  due  to  pyrite.  The  iron  content  may,  after  the 
best  work,  reach  a  much  higher  figure,  due  to  the  presence  of  com- 
bined iron  in  the  blende.  The  Joplin  and  Wisconsin  ores  usually 
do  not  carry  to  exceed  J  per  cent,  combined  iron.  The  Leadville 
ores  offer  a  more  difficult  problem,  owing  to  the  presence  of  blende 
of  all  degrees  of  permeability :  an  extraction  of  75  to  85  per  cent, 
in  a  product  carrying  40  to  50  per  cent,  zinc  is  good  work.  Direct 


120  ELECTRO-MAGNETIC   ORE   SEPARATION 

separation  of  these  ores  yields  a  lower  grade  product  and  a  less 
extraction. 


SEPARATION  OF  MAGNETIC  BLENDE  FROM  PYRITE 

Magnetic  blende  is  of  frequent  occurrence  at  Leadville,  Col- 
orado, and  other  parts  of  the  Rocky  Mountain  region,  and  is  also 
found  in  important  ore  bodies  in  Europe  and  Australia.  The  Col- 
orado ores  of  this  type  usually  carry  galena,  sphalerite,  and  pyrite 
with  subordinate  amounts  of  pyrrhotite;  the  galena  is  usually  ar- 
gentiferous and  the  pyrite  may  or  may  not  carry  the  precious 
metals.  The  sulphide  of  zinc  in  these  ores  varies  from  straw-col- 
ored blende  to  marmatite — in  other  words,  from  a  nonmagnetic 
mineral  to  one  possessing  sufficient  permeability  to  be  removed 
magnetically  in  its  raw  state. 

The  determination  of  a  process  for  the  treatment  of  any  ore 
carrying  magnetic  blende  should  be  done  by  actual  test  on  suffi- 
ciently large  samples  to  indicate  commercial  results.  If  the 
blende  is  wholly  or  in  large  part  magnetic,  then  a  direct  separation 
on  high-intensity  separators  is  in  order.  Individual  particles  of 
marmatite  may  show  ferromagnetism,  but  the  bulk  of  the  mineral 
in  an  ore  is  usually  less  strongly  magnetic,  and  a  field  of  high 
intensity  is  necessary  to  obtain  a  satisfactory  recovery.  The  value 
of  the  pyrite  in  gold  and  silver  plays  an  important  part  in  the 
determination  of  the  process  to  be  followed;  if  its  value  is  neg- 
ligible, then  any  loss  of  blende  in  the  nonmagnetic  tailing  merely 
results  in  a  decrease  in  the  percentage  recovery  of  the  zinc ;  but  if 
the  pyrite  is  valuable  for  contained  gold  and  silver,  this  nonmag- 
netic tailing  should  be  kept  below  the  zinc  penalty  limit  set  by  the 
lead  smelters  to  which  this  product  is  destined.  In  choosing  be- 
tween direct  separation  and  separation  after  roasting,  the  higher 
value  at  the  smelter  of  roasted  pyrite  over  the  raw  sulphide  should 
be  considered. 

At  one  plant  treating  marmatite  ores,  the  nonmagnetic  blende 
remaining  in  the  pyrite  tailing  is  removed  by  electrostatic  sep- 
arators. When  there  is  much  of  this  nonmagnetic  blende  in  an 
ore,  and  the  value  of  the  pyrite  in  gold  and  silver  is  sufficient,  the 
nonmagnetic  tailing  may  be  roasted,  and  the  iron  and  blende  re- 
covered separately  as  clean  products.  With  ores  which  require 
roasting,  a  preliminary  treatment  of  the  raw  ore  on  magnetic  sep- 


THE   SEPARATION  OF  PYRITE  AND  BLENDE 


121 


arators  to  remove  the  strongly  magnetic  marmatite  is  advisable,  as 
the  actual  passing  of  the  ore  over  a  separator  represents  but  a  very 
small  proportion  of  the  total  cost  of  preparing  the  ore  for  mag- 
netic treatment,  and  this  magnetic  blende  would  otherwise  find  its 
way  into  the  roasted  iron  tailing. 

At  Koleomo,  Colorado,  the  Kimberly-Wilfley  Mines  Co.  is  sep- 
arating pyrite  from  galena  and  blende  after  roasting  to  the  mag- 


FIG.    59.  — WILFLEY   ROASTING   FURNACE. 

A,  Fire  box;  B,  up-cast  flue;  C,  down-cast  or  roasting  flue;  D1,  D2,  D3,  D4,  water-jackets; 
E,  water-jacket  screw  conveyor;  F,  dust  chamber;  G,  dust  flue;  H,  stack;  7,  feed  opening; 
J,  ore  feeder. 


netic  sulphide.  The  ore  carries  galena,  slightly  magnetic  blende, 
and  pyrite  containing  gold  and  silver  values.  The  ore  from  the 
mine,  after  passing  through  a  breaker,  is  crushed  by  16  X  42-in. 
rolls  to  f  in.  and  is  then  sized  and  gradually  reduced  to  14  mesh 
by  three  sets  of  12  X  36-in.  rolls.  The  crushed  ore  is  transported 
by  a  conveyor  belt  to  a  Wilfley  roasting  furnace,  a  cross  section  of 
which  is  shown  in  the  accompanying  figure.  ; 

The  ore  fed  at  the  top  of  the  furnace  falls  upon  a  plate  set  at 
an  angle  of  50  degrees,  thence  through  the  down-cast  flue,  striking 
upon  water-cooled  plates,  and  finally  into  a  water-jacketed  screw; 


122  ELECTRO-MAGNETIC  ORE   SEPARATION 

conveyor  which  discharges  it  from  the  furnace.  The  roasting  is 
carried  out  by  the  hot  gases  from  the  fire  box  together  with  the  heat 
generated  by  the  oxidizing  pyrite  upon  individual  particles,  which 
are  cooled  to  a  certain  extent  before  coming  into  contact  with  other 
particles,  preventing  fritting,  and  gives  a  uniform  roast  to  the 
small  and  large  particles  alike.  The  ore  is  cooled  sufficiently  before 
passing  out  of  the  furnace  to  prevent  a  continuance  of  the  oxida- 
tion when  it  comes  into  contact  with  the  atmosphere.  The  dust 


FIG.   60.  — DINGS   SEPARATORS   AT  KOKOMO,   COLORADO. 

is  collected  in  F  and  G,  and  is  discharged  from  the  furnace  by  a 
screw  conveyor. 

The  fuel  consumption  is  low,  most  of  the  heat  necessary  for 
the  roasting  being  generated  by  the  oxidation  of  the  pyrite,  the 
coal  being  used  to  regulate  the  temperature  of  the  roast.  It  is 
said  that  during  steady  operation  the  temperature  of  the  roasting 
flue  does  not  vary  more  than  10  degrees,  and  a  variation  in  the 
feed  does  not  cause  a  variation  of  more  than  100  degrees.  The 
temperature  is  indicated  by  a  pyrometer,  the  thermal  couple  being 
placed  in  the  roasting  flue  above  the  water  jackets. 

The  ore,  as  delivered  from  the  furnace,  is  elevated  and  passed 
through  a  water-jacketed  revolving  cylindrical  cooler,  in  which  the 
temperature  of  the  ore  is  reduced  to  60°  F.,  and  sent  to  the  sepa- 
rator bins.  Ten  Dings  separators  are  employed  to  effect  the 
separation  of  the  roasted  ore.  The  magnetic  iron  product  from 
these  separators  falls  upon  a  belt  conveyor  which  delivers  to  ship- 


THE   SEPARATION  OF  PYRITE  AND  BLENDE  123 

ping  bins,  whence  it  is  shipped  to  the  lead  smelters.  The  nonmag- 
netic product  falls  upon  another  belt  conveyor  delivering  to  an 
elevator,  is  mixed  with  water  and  passed  to  two  Richards  classi- 
fiers, making  four  sizes ;  thence  it  is  fed  to  eight  Wilfley  roughing 
tables.  The  pulp  and  middlings  are  sent  to  eight  other  Wilfley 
tables  placed  on  the  floor  below  and  directly  beneath  the  roughing 
tables.  The  tabling  plant  is  operated  in  two  units  of  eight  tables 
each :  one  lower  table  receives  all  the  zinc  middlings,  one  all  the  lead 
middlings,  one  all  the  iron  middlings  not  rendered  magnetic  in 
the  roast,  and  one  all  the  silica  middlings  from  four  of  the  rough- 
ing tables  above.  The  overflow  from  the  classifiers,  the  crosswash 
from  the  feed  end  of  the  Wilfley  tables,  and  the  dust  from  the 
furnace  go  to  a  Buckingham  filter  tank,  which  classifies  and  de- 
waters  the  fines  and  makes  a  thick  pulp  that  is  fed  to  a  Wilfley 
table  and  to  a  True  vanner  fitted  with  egg-shell  belt.  It  is  stated 
that  the  roasting  of  the  ore  so  changes  the  galena  and  blende  that 
even  the  finest  particles  will  not  float,  and  renders  easy  an  other- 
wise difficult  separation.1 

The  plant  has  a  capacity  of  250  tons  per  day. 

At  Denver,  Colorado?  the  Colorado  Zinc  Co.  is  operating  a 
plant  of  100  tons  daily  capacity,  equipped  with  a  Wilfley  furnace 
and  Dings  separators,  with  Wilfley  tables  for  the  separation  of  the 
nonmagnetic  product.  The  ore  is  crushed  dry  to  16  mesh,  passed 
through  the  furnace  where  from  10  to  15  per  cent,  sulphur  is 
driven  off,  transforming  the  pyrite  to  the  magnetic  sulphide.  Af- 
ter cooling  in  a  water-jacketed  cylindrical  cooler,  the  ore  is  passed 
over  4  Dings  separators  which  remove  the  iron,  amounting  to  from 
40  to  50  per  cent,  of  the  ore,  while  the  nonmagnetic  product  is  sent 
to  the  tables.  The  furnace  is  8  X  8  ft.  in  section  and  30  ft.  high, 
and  has  a  capacity  of  100  tons  per  24  hours.  With  ore  carrying 
25  per  cent,  iron  as  pyrite  the  furnace  requires  1  ton  of  coal  per 
day  when  operated  at  capacity.  The  separators  deliver  a  finished 
iron  product  and  a  silica-zinc-lead  middling  which  is  sent,  after 
sizing,  to  four  Wilfley  tables;  these  tables  are  operated  to  make 
finished  zinc  concentrate,  while  the  lead-zinc  middling  and  the 
silica-zinc  middling  are  re-treated  on  three  other  tables.  It  is 
stated  that,  due  to  the  action  of  the  roast,  the  galena  and  blende 

1  Communicated  by  F.  W.  Gregory,  Kokomo,  Colorado,  and  from  E.  &  M. 
J.,  vol.  Ixxxv,  p.  453.     J.  M.  McClave. 

'E.  &  M.  J.,  vol.  Ixxxv,  p.  453.    J.  M.  McClave. 


124  ELECTRO-MAGNETIC  ORE   SEPARATION 

do  not,  in  the  finest  particles,  float,  and  that  the  wash-water  from 
the  tables  runs  clear,  while  when  the  ore  is  tabled  without  roasting 
the  wash  water  contains  from  10  to  15  per  cent,  of  lead-zinc  slime. 

At  Galena,  Illinois,  the  Joplin  Separating  Co.  is  operating  a 
custom  plant  whose  raw  material  is  derived  from  the  adjacent 
Wisconsin  zinc  field.  Zinc-iron  concentrate  from  mills  not  equipped 
with  separating  plants  forms  the  greater  part  of  the  material 
treated;  raw  ores  carrying  zinc,  iron,  and  lead  sulphides  are  also 
purchased  and,  after  water  concentration,  magnetically  cleaned. 

This  plant  is  well  managed  and,  although  running  on  all 
grades  and  classes  of  material,  probably  represents  the  best  practise 
of  the  district.  The  mill  includes  a  roasting  furnace  of  40  tons 
capacity  per  24  hours,  three  Cleveland-Knowles  12-in.  belt  sep- 
arators, and  a  complete  equipment  of  jigs,  tables,  etc.,  for  the 
concentration  of  raw  ores  preliminary  to  roasting  and  magnetic 
separation. 

The  Wisconsin  ores  carry  blende,  galena  and  marcasite  in  a 
limestone  gangue.  The  ore  is  easily  crushed  and  yields  the  bulk 
of  its  component  minerals  when  crushed  to  4  mesh,  although  a 
finer  comminution  is  carried  out  on  the  middling  products  from 
the  jigs.  The  blende  is  of  the  variety  known  as  "  rosin  jack,"  and 
rarely  carries  to  exceed  -J  per  cent,  combined  iron:  some  darker- 
colored  blende  is  produced  in  the  district,  but  none  that  came 
under  the  writer's  observation  was  sufficiently  magnetic  to  be 
affected  by  the  low-intensity  magnetic  fields  employed  in  the  sep- 
aration of  these  ores.  The  purity  of  the  ores  is  well  illustrated  by 
the  fact  that  60  per  cent,  concentrate  is  the  standard  grade  from 
which  prices  are  figured,  and  iron  in  excess  of  2  per  cent,  is  pen- 
alized at  the  rate  of  $1  per  unit. 

In  this  mill  the  blende-marcasite  concentrate  is  delivered  to 
the  feed  hopper  above  the  roasting  furnace  by  a  6-in.  bucket  ele- 
tator.  The  feed  hopper  is  36  ins.  square  and  slopes  from  two  sides 
to  a  point.  The  feeder,  of  the  stirrup  type,  delivers  into  a  sheet- 
iron  spout  which  extends  well  into  the  neck  of  the  furnace. 

The  furnace  is  of  the  revolving-cylinder  type,  built  by  the 
Galena  Iron  Works,  and  is  32  ft.  long  by  5  ft.  in  diameter.  It 
is  built  of  boiler  plate  and  lined  with  fire  brick.  This  shell  is 
fitted  with  two  tires  which  rest  upon  two  sets  of  rollers,  the  dis- 
tance apart  of  which  may  be  adjusted  to  give  any  desired  inclina- 
tion from  the  horizontal  to  the  axis  of  the  cylinder,  so  accelerating 


THE  SEPARATION  OF  PYRITE  AND  BLENDE  125 

or  retarding  the  passage  of  the  ore  through  it.  Revolution  is  im- 
parted to  the  cylinder  by  gearing.  At  either  end  the  furnace  is  nar- 
rowed by  fire-brick  walls  to  2  ft.  6  ins.  for  connection  with  the 
fire  box  at  the  discharge  end,  and  with  the  dust  chamber,  which 
also  serves  as  foundation  for  the  stack,  at  the  feed  end.  These  con- 
nections are  made  through  cast-iron  necks  projecting  into  the 
openings  at  each  end  of  the  cylinder.  The  fire  box  is  fitted  with  a, 
grate  4X5  ft.  in  area,  which  burns  about  two  tons  of  soft  coal 
in  24  hours.  The  roasted  ore  is  discharged  through  the  annular 
opening  between  the  projecting  neck  of  the  fire  box  and  the  end  of 
the  cylinder.  A  fire-brick  wall  reaching  the  horizontal  diameter 
of  the  fire-box  neck  causes  the  hot  gases  to  impinge  on  the  roof  of 
the  cylinder  and  not  to  strike  the  hot  ore. 

A  24-in.  rotary  blower  is  mounted  alongside  the  furnace  and 
suitably  connected  to  furnish  air  under  pressure  beneath  the  grate. 
This  is  useful  in  raising  the  temperature  of  the  charge  quickly 
should  it  fall  below  normal  and  an  imperfectly  roasted  product  be 
likely  to  result. 

The  roasted  ore  discharged  from  the  furnace  falls  upon  a  cast- 
iron  plate,  and  is  conveyed  to  one  side  by  scrapers  mounted  upon 
a  traveling  chain,  and  falls  into  wheelbarrows. 

The  furnace  makes  two  revolutions  in  three  minutes,  the  ore 
remaining  in  it  for  approximately  two  and  one  half  hours. 

The  hot  ore  is  wheeled  to  a  cooling  floor  26  ft.  wide  by  60  ft. 
long;  here  it  is  spread  a  few  inches  deep  and  allowed  to  remain  12- 
hours.  The  ore  was  formerly  cooled  by  means  of  a  spray  of  water,, 
but  this  gave  rise  to  an  excessive  amount  of  fines,  produced  by  the 
sudden  cooling,  so  that  it  was  abandoned  in  favor  of  the  cooling 
floor,  in  spite  of  the  increased  cost  of  handling  entailed. 

The  cooled  roasted  material  is  raised  to  the  top  of  the  mill  by  a 
bucket  elevator  and  fed  into  a  trommel  36  ins.  in  diameter.  This- 
trommel  is  fitted  with  two  screens,  each  delivering  its  undersize 
to  a  separate  bin,  while  the  oversize  from  both  is  crushed  in  tight 
rolls  and  returned.  The  first  screen  has  g*g-in.  and  the  second  -ft-in. 
round  punched  holes. 

The  roasted  concentrate  passing  -^-in.  is  treated  on  separator 
No.  1,  which  carries  }  ampere  on  the  first  magnet  and  6.5  amperes 
on  the  second,  making  a  clean  iron  tailing  product  and  a  clean 
nonmagnetic  zinc  product.  The  material  between  ^  and  fVin.  is 
treated  on  separator  No.  2,  which  carries  the  same  current,  re- 


126  ELECTRO-MAGNETIC  ORE  SEPARATION 


FLOW   SHEET 
Raw  concentrate 

elevator  No.  1 

hopper  by  automatic  feeder  to 
5  ft.  X  32  ft.  cylindrical  roasting  furnace 

by  wheelbarrow  to 
26  ft.  X  60  ft.  cooling  floor 

by  wheelbarrow  to 
oversize  tight  rolls        elevator  No.  2 

trommel,  -ft-in.  holes  and  &-in.  holes 

through  A-in.  through  ^/-in. 

separator  No.  2  separator  No.  1 


I  I  I  I  I  I 

1st  magnet    2d  magnet    nonmagnetic    1st  magnet    2d  magnet    nonmagnetic 

[tailing]  middling  [grade  A  zinc  conct.]  [tailing]  middling  [grade  B  zinc  conct.] 

middling  rolls,  set  tight 
elevator  No.  3 
i^-in.  trommel 

through 
oversize  | 

separator  No.  3 


1st  magnet  2d  magnet  nonmagnetic 

[tailing]  middling  to  tables        returned  to  furnace 


spectively,.  on  the  two  magnets.  The  middling  product  from  both 
these  machines  is  crushed  in  tight  rolls  to  ^  in.,  and  fed  to  sep- 
arator No.  3,  which  also  makes  three  products.  The  tailing  from 
the  first  magnet  is  discarded  while  the  middling  from  the  second 
magnet  is  sent  to  the  tables  in  the  concentration  mill.  The  non- 
magnetic product  from  this  separator  carries  most  of  its  iron  as 
unchanged  pyrite,  liberated  by  the  recrushing  of  the  middling 
from  separators  Nos.  1  and  2,  and  is,  therefore,  fed  back  to  the 
roasting  furnace. 


THE  SEPARATION  OF'PYRITE  AND  BLENDE  127 

The  speeds  of  the  separator  belts  are  adjusted  to  suit  each 
class  of  material  treated. 

The  magnetic  tailing  is  run  to  waste  through  a  launder  in 
which  a  stream  of  water  is  kept  flowing,  and  the  cleaned  blende  is 
delivered  to  shipping  bins  through  chutes. 

The  finished  product  is  sold  under  two  grades:  grade  "A" 
is  the  product  from  the  separator  treating  the  coarser  size  and 
grade  "  B  "  from  that  treating  the  finer  size ;  it  has  been  found 
here  that  the  coarser  the  size  of  the  concentrate  the  higher  the 
grade.  The  average  selling  assays  on  33  car  loads  gave  grade  A 
60.49  per  cent,  zinc  and  2.11  per  cent,  iron,  and  grade  B  57.07  per 
cent,  zinc  and  2.19  per  cent.  iron.  The  total  amount  shipped  was 
in  the  proportion  of  two  cars  of  B  to  each  car  of  A. 

The  raw  concentrate  purchased  by  this  mill  carries  from  11 
to  33  per  cent.  zinc.  The  tailing  produced  averages  below  5  per 
cent.,  which  figure  is  said  to  be  never  exceeded.  The  efficiency  of 
the  plant  is  given  as  85  per  cent,  of  the  zinc  in  the  raw  concentrate. 

The  mill  is  equipped  with  a  complete  series  of  rheostats  to 
control  the  currents  on  all  magnets  from  the  central  switch- 
board. 

At  Hazel  Green,  Wisconsin,  the  Kennedy  Mining  Co.  employs 
a  Cleveland-Knowles  separator  to  clean  roasted  blende-marcasite 
concentrate.  The  concentration  mill  treats  100  tons  of  ore  daily 
for  a  production  of  25  tons  of  concentrate,  carrying  from  41  to 
42  per  cent.  zinc.  From  the  mill  the  concentrate  is  delivered  to 
the  roaster  building  by  a  self-dumping  skip  and  drops  into  the 
boot  of  a  bucket  elevator,  which  delivers  to  the  furnace  feed  hop- 
per. The  furnace  is  of  the  cylindrical  type  usual  in  the  Wisconsin 
district  and  is  28  ft.  long  and  5  ft.  in  diameter.  It  is  set  at  an 
inclination  of  4  ins.  in  28  ft.  and  makes  two  revolutions  in  3 
minutes.  The  ore  remains  in  the  furnace  from  3J  to  4  hours. 
The  cylinder  is  lined  with  8-in.  fire  brick  between  which  are  set 
at  intervals  projections  of  refractory  material  in  the  form  of  equi- 
lateral triangles  with  an  altitude  of  3  ins.,  which  serve  to  lift  the 
ore  by  the  revolution  of  the  furnace  and  allow  it  to  fall  through 
the  hot  gases  from  the  fire  box.  About  two  tons  of  soft  coal  are 
burned  in  24  hours.  The  roasted  concentrate  falls  from  the  fur- 
nace into  a  paddle  conveyor,  where  it  is  sprayed  with  water,  which 
is  evaporated  immediately  by  the  hot  material,  which  it  serves  to 
cool.  This  conveyor  delivers  to  a  bucket  elevator  delivering  into 


128  ELECTRO-MAGNETIC  ORE  SEPARATION 

a  trommel  above  the  separator  bins.  The  roasted  concentrate  is 
here  sized  into  two  products,  through  j^  in.  and  between  T^  in. 
and  J  in. ;  these  two  sizes  are  treated  at  different  times  by  the 
separator  and  the  oversize  is  recrushed.  The  first  magnet  of  the 
separator,  which  is  a  21-in.  Cleveland-Knowles  machine,  takes  1.5 
amperes  and  the  second  magnet  3.5  amperes.  The  separator  belt 
travels  at  a  speed  of  about  175  ft.  per  minute.  The  magnets  revolve 
at  75  R.P.M.  at  a  height  of  1  in.  above  the  belt.  The  separator 
treats  from  20  to  22  tons  of  roasted  concentrate  in  24  hours,  which 
indicates  a  burden  of  from  1.25  to  1.5  Ibs.  of  material  on  the 
belt  at  any  one  time;  this  quantity  is  carried  as  an  even  layer  one 
particle  deep.  The  first  magnet  takes  out  an  iron-tailing  product 
which  is  run  to  waste  in  a  launder;  the  second  magnet  removes  a 
middling  product  which  is  fed  to  the  middling  rolls  in  the  concen- 
tration mill — a  procedure  of  doubtful  economy.  The  nonmagnetic 
material  remaining  on  the  belt  is  almost  clean  blende,  with  a 
little  limestone  and  galena  which  were  not  eliminated  in  the  con- 
centration mill,  and  not  being  magnetic,  these  are  concentrated  by 
the  separation  in  the  same  proportion  as  the  blende.  The  cleaned 
zinc  product  amounts  to  about  16.5  tons  in  24  hours  and  assays  60 
per  cent,  zinc  with  2  per  cent.  iron.  The  tailing  carries  about  5 
per  cent.  zinc. 

At  Platteville,  Wisconsin,  the  Enterprise  Mining  Co.  is  separat- 
ing about  15  tons  of  blende-marcasite  concentrate  daily.  The  con- 
centrate is  delivered  from  the  mill  to  the  roaster  bin  by  a  skip  run- 
ning on  an  incline.  The  Galena  cylindrical  roasting  furnace  is 
employed,  the  concentrate  remaining  in  the  furnace  three  hours. 
The  roasted  concentrate  is  sized  in  a  trommel  into  three  products : 
through  -J  in.,  between  £  in.  and  J  in.,  and  oversize.  The  first 
two  are  fed  to  a  21-in.  Cleveland-Knowles  separator  separately, 
the  bin  being  provided  with  a  partition  to  keep  them  apart;  the 
^-in.  oversize  is  crushed  and  refed  to  the  furnace.  The  separator 
carries  3  amperes  on  the  first  magnet  and  5  amperes  on  the  sec- 
ond. The  tailing  from  the  first  magnet  is  run  to  waste  in  a  wet 
launder  and  the  middling  from  the  second  magnet  sent  to  the  jigs 
in  the  concentrating  mill ;  a  falling  off  in  the  average  grade  of  the 
cleaned  zinc  product  from  61  to  59  per  cent,  is  said  to  have  re- 
sulted from  so  treating  the  middling.  The  cleaned  zinc  concen- 
trate carries  from  58  to  62  per  cent,  zinc  and  averages  about  2  per 
cent.  iron.  The  raw  concentrate  fed  to  the  furnace  carries  from  40 


THE   SEPARATION  OF  PYRITE  AND  BLENDE  129 

to  45  per  cent.  zinc.  The  tailing  from  the  separator  is  said  to 
carry  4.5  per  cent.  zinc. 

The  Empire  Mining  Co.,  of  Platteville,  is  operating  a  plant 
similarly  equipped.  From  18  to  20  tons  of  raw  blende-marcasite 
concentrate  is  treated  daily  for  a  recovery  of  from  10  to  15  tons  of 
cleaned  zinc.  The  cleaned  zinc  concentrate  carries  from  60  to  63 
per  cent,  zinc  and  from  1  to  3  per  cent.  iron.  Hocking  Valley  Coal 
is  burned  by  the  furnace,  costing  $5  per  ton  delivered;  the  fur- 
nace uses  from  1500  to  2000  Ibs.  in  24  hours. 

At  Mineral  Point,  Wisconsin,  the  Mineral  Point  Zinc  Co.  op- 
erates a  custom  magnetic-separating  plant  in  conjunction  with  a 
zinc-reduction  works.  The  raw  material  is  gathered  from  all  parts 
of  the  district  and  consists  chiefly  of  the  products  of  water  con- 
centration ranging  in  size  from  J  in.  downward;  crude  ore  is  oc- 
casionally treated.  The  concentrate  fed  to  the  furnace  ranges 
from  28  to  34  per  cent.  zinc. 

The  roasting  plant  is  equipped  with  two  cylindrical  furnaces  of 
the  Galena  type,  only  one  of  which  is  at  present  in  use.  This  is 
20  ft.  long  by  5  ft.  in  diameter.  The  lining  of  this  furnace  is  of 
8-in.  special-arch  fire  brick  in  which  are  set  four  rows  of  10-in. 
brick  spaced  90  degrees  apart;  these  elongated  brick  serve  to  lift 
the  ore  by  revolution  of  the  furnace  and  allow  it  to  fall  through 
the  hot  gases ;  the  substitution  of  14-in.  brick  in  place  of  the  10-in. 
is  contemplated.  This  furnace  is  equipped  with  a  dust  chamber 
5  ft.  4  in.  wide  by  14  ft.  in  length,  is  divided  horizontally  by  a 
plate  of  heavy  sheet  iron.  The  gases  from  the  furnace  pass  into 
the  lower  compartment  of  the  dust  chamber,  along  beneath  the 
plate  to  the  farther  end,  where  a  2-ft.  space  is  left  between  the 
end  of  the  plate  and  the  wall  of  the  dust  chamber,  and  thence 
back  over  their  course,  but  above  the  plate,  to  the  stack,  which 
is  30  ins.  in  diameter  and  50  ft.  high.  The  dust  is  removed 
through  three  doors,  two  on  the  upper  level,  and  one  on  the  lower, 
each  12  ins.  wide  by  2  ft.  high.  The  fire-box  grate  is  4  X  5  ft.  in 
area,  and  burns  from  1.5  to  2  tons  of  soft  coal,  costing  $3  per 
ton,  daily.  The  cylinder  makes  one  revolution  in  50  seconds,  the 
ore  remaining  in  the  furnace  from  3  to  3.5  hours.  The  temperature 
of  the  roast  is  just  sufficient  to  start  a  slight  fritting  at  the  dis- 
charge neck  of  the  furnace;  that  this  action  is  incipient  is  shown 
by  the  fact  that  little  trouble  is  experienced  from  overroasting  or 
from  particles  of  zinc  and  iron  which  have  been  cemented  together. 


130 


ELECTRO-MAGNETIC  ORE   SEPARATION 


The  slight  deposit  which  forms  at  the  discharge  neck  is  removed 
from  time  to  time  with  a  long  chisel.  Paddle-and-chain  conveyors 
are  used  to  convey  the  roasted  ore  from  the  furnace,  and  a  small 
stream  of  water  is  sprayed  upon  the  hot  material  to  lay  the  dust 
and  assist  in  cooling  it;  the  water  used  is  regulated  so  that  it 
may  be  completely  evaporated  by  the  heat  of  the  ore  before  it 


FIG.   61.  — MILL   OF  THE   TRIPOLI  MINING  CO.,  MINERAL   POINT,  WIS. 


reaches  the  separator  bins.     The  furnace  treats  about  twenty  tons 
of  raw  concentrate  in  24  hours. 

The  roasted  concentrate  is  separated  on  a  Cleveland-Knowles 
21-in.  separator  and  upon  a  Dings  separator,  set  up  side  by  side 
and  working  on  the  same  material.  Either  machine  is  capable 
of  treating  the  output  from  one  surface.  The  Cleveland-Knowles 
carries  3  amperes  on  the  first  magnet  and  6  amperes  on  the  second : 
the  Dings  separator  carries  3  amperes  on  either  magnet.  The 
roasted  concentrate  is  sized  before  separation  into  two  products, 
between  =J  and  \  in.,  and  through  J  in.  The  concentrate  averages 
59  per  cent,  zinc  and  2.5  per  cent,  iron;  the  middling  amounts  to 


THE  SEPARATION  OF  PYRITE  AND  BLENDE 


131 


||I 

• 

• 

i-H 

S8S 

» 

. 

» 

a 

8 

• 

« 

• 

Separator 

% 

L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

2-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 
ings  
L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

I  -in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

L-in.  Cleveland-Knowles. 

<N 

<N 

^ 

<N    Q    c* 

<N 

<N 

<N 

<N 

<N 

<N 

<N 

Q 

g, 

. 

. 

S 

j      | 

1 

O 

Name  of  Company 

I 

O 

fcc 

d 

"8 

s 

d 
O 

w 

Murphy  Mining  and  Development  C( 

Rowley  Mining  Company  

Winnebago  Mining  Company  
Amalgamated  Zinc  Mines  Company. 
Dawson  Mining  Company  

Blackhawk  Mining  Company  

Gritty  Six  Mining  Company  

Reliable  Mining  Company  

.S 

1 
1 

Morrison  Mining  and  Development  C 

Union  Zinc  and  Lead  Company  

Brown  &  Croft  Mining  Co  

Hazel  Patch  Mining  Company  

2 

i 

d 

d 

4a 

O 

O 
1 

Buncombe 

Buncombe 
Benton  .  .  . 
Benton  .  .  . 

.£P 

O 

1 

B 

o 

o 
1 

Schullsburg 

Schullsburg 

Schullsburg 

Is 
1 

3 

132  ELECTRO-MAGNETIC  ORE   SEPARATION 

from  7  to  10  per  cent,  of  the  feed  and  carries  17  per  cent,  zinc;  it 
is  stacked  awaiting  a  process.  The  tailing  product  averages  from 
2  to  2.25  per  cent.  zinc.  An  efficiency  of  from  85  to  86  per  cent, 
of  the  zinc  in  the  raw  concentrate  recovered  in  the  cleaned  zinc 
product  is  claimed  for  the  plant. 

Power  for  the  furnace  and  separators  is  supplied  by  a  15  H.P. 
motor. 

The  mill  of  the  Tripoli  Mining  Co.,  situate  three  miles  north- 
west of  Mineral  Point,  is  separating  blende-marcasite  concentrate 
on  Dings  separators.  The  concentrate  from  the  inill  is  trammed 
to  the  roaster  building,  some  200  ft.  away,  in  mine  cars,  and 
dumped  at  the  foot  of  a  bucket  elevator  delivering  to  the  furnace 
feed  hopper.  The  furnace,  of  the  cylindrical  type,  makes  one  revo- 
lijtion  in  1  minute  and  40  seconds  and  roasts  from  18  to  20  tons  of 
concentrate  in  24  hours.  The  roasted  ore  from  the  furnace  falls 
into  a  screw  conveyor  15  ins.  in  diameter  and  making  24  E.P.M., 
and  from  this  into  a  chain  conveyor  running  at  a  speed  of  2  ft.  per 
second;  there  are  23  ft.  of  screw  conveyor  and  15  ft.  of  chain  con- 
veyor, and  in  this  distance  the  roasted  material  is  sufficiently  cooled 
to  be  fed  into  the  separator  bins.  A  noticeable  grindmg  action  is 
set  up  in  these  conveyors. 

The  roasted  concentrate  is  separated  on  a  Dings  separator. 
The  raw  concentrate  carries  from  30  to  35  per  cent,  zinc,  and  the 
cleaned  zinc  product  from  the  separator  from  57  to  59  per  cent, 
zinc  with  from  2.5  to  5  per  cent.  iron. 

A  motor  taking  44  amperes  at  125  volts  drives  the  furnace, 
conveyors,  elevators,  separator,  etc. 

At  Joplin,  Missouri,  the  Joplin  Separating  Co.  is  operating  a 
custom  separating  plant  on  blende  concentrate.  The  iron  content 
of  the  raw  concentrate  averages  15  per  cent.,  which  is  reduced  to 
an  average  of  1.06  per  cent,  in  the  cleaned  zinc  product.  The 
roasting  is  done  in  kilns,  and  the  separation  on  two  Cleveland- 
Knowles  separators. 

At  Kaslo,  British  Columbia,  the  Kootenay  Ore  Works  operates 
a  custom  works  on  concentrate  carrying  galena,  blende  and  pyrite 
carrying  from  15  to  20  per  cent,  iron  and  rarely  exceeding  37  per 
cent.  zinc.  The  ore  is  delivered  from  railroad  cars  to  bins  at  the 
top  of  the  mill  and  after  passing  a  sampler  is  fed  to  a  White- 
Howell  roasting  furnace.  The  roasted  ore  is  cooled  in  a  revolving 
cylinder  through  which  a  current  of  cold  air  is  passed.  After 


THE   SEPARATION  OF   PYRITE  AND  BLENDE 


133 


cooling,  the  ore  is  crushed  to  pass  20  mesh  and  classified  into  eight 
sizes,  and  the  iron  removed  on  four  Dings  separators.  The  final 
zinc  product  carries  from  7  to  8  per  cent.  iron. 

At  Huanchaca,  Bolivia,  "  Stern  "  type  separators  are  employed 
to  separate  blende-pyrite  ores  after  roasting.  There  are  five  of 
these  machines  in  operation;  three  of  them  treat  original  ore,  and 
two  others  are  used  to  clean  the  concentrates  from  the  first  ma- 
chines. The  capacity  of  the  plant  is  2  metric  tons  per  hour. 

The  ore  from  the  mine  is  crushed  to  30  mm.  in  a  breaker, 


FIG.   62.  — KOOTENAY  ORE  WORKS,  KASLO,  B.C. 


which  is   followed  by  rolls,  further  reducing  the  ore  to  pass  a 
4-mm.  screen. 

From  the  rolls  the  ore  is  lifted  by  a  bucket  elevator  and  fed  to 
a  roasting  furnace  of  the  revolving-cylinder  type.  The  roast  drives 
off  sulphur  from  the  pyrite,  forming  the  magnetic  oxide  of  iron. 
The  roasted  ore  is  let  fall  into  a  conveyor,  where  it  is  cooled  by  the 
action  of  a  stream  of  cold  water,  and  thence  is  carried  to  a  trom- 
mel with  4-mm.  screens.  The  oversize,  due  to  swelling  in  the 
roast,  is  returned  to  the  rolls,  while  the  material  which  passes  the 
screen  is  delivered  to  feed  hoppers  supplying  the  separators.  The 
ore  at  this  point  is  mixed  with  the  proper  quantity  of  water  in  a 
specially  constructed  funnel  mixer,  and  next  fed  to  the  roughing 
separators,  three  of  the  Stern-type  wet  machines. 


134  ELECTRO-MAGNETIC  ORE  SEPARATION 

The  nonmagnetic  blende  is  caught  in  a  trough  beneath  the  sep- 
arators and  after  settling  is  drawn  off,  constituting  a  finished 
product.  The  magnetic  roasted  iron  is  delivered  to  a  tube  mill  and 
reduced  to  2  mm.,  and  from  thence  is  elevated  by  a  centrifugal 
pump  to  settling  tanks  from  which  it  is  tapped  to  the  cleaning  sep- 
arators, two  in  number,  of  the  same  type  as  the  machines  working 
on  raw  ore. 

The  final  results  of  the  magnetic  separation  are  a  concentrate 
carrying  50.81  per  cent,  zinc  and  tailing  averaging  3.98  per  cent, 
zinc;  the  feed  averages  30.81  per  cent,  and  the  extraction  in  terms 
of  total  zinc  in  the  feed  is  98  per  cent.  On  a  somewhat  lower 
grade  of  ore  the  following  results  are  obtained :  concentrate,  40.10 
per  cent,  zinc;  tailing  4.80  per  cent,  zinc;  the  feed  averaging  24.22 
per  cent,  and  the  extraction  91.3  per  cent. 

At  Pueblo,  Colorado,  the  Mechernich  separator  is  employed  by 
the  United  States  Zinc  Co.  for  the  separation  of  blende  from  py- 
rites, and  the  other  mixed  sulphides.  The  ore  is  given  a  roast 
preliminary  to  separation. 

At  Ravalo,1  Sweden,  Herbele  separators  are  employed  to  sep- 
arate zinc-iron-lead  ores. 

At  Munsterbusch,  near  Stolberg,  Germany,  the  Aktien-Gesell- 
schaft  fur  Bergbau-Blei  und  Zinkfabrikation  is  separating  roasted 
blende-pyrite  concentrate  on  an  80-cm.  Mechernich  separator. 

At  Hamborn,  Germany,  the  Aktien-Gesellschaft  fur  Zink-In- 
dustrie  is  operating  a  plant  equipped  with  Humboldt-Wetherill 
separators  on  blende-pyrite  concentrate. 

At  Lipine,  Upper  Silesia,  Germany,  the  Schlesischen  Aktien- 
Gesellschaft  is  separating  roasted  blende-pyrite  concentrate  on 
Mechernich  separators.  The  raw  material  carries  from  25  to  26 
per  cent  zinc,  which,  after  a  slight  roast,  is  passed  over  a  Mecher- 
nich double-pole  separator.  This  machine  treats  an  average  of 
1.5  metric  tons  per  hour  from  which  is  produced  0.9  ton  of  zinc 
product  assaying  about  40  per  cent,  and  0.6  ton  iron  product  as- 
saying 15  per  cent,  zinc,  indicating  an  extraction  of  80  per  cent. 

At  Carlshof,  Germany,  Henckel  von  Donnersmark  is  operating 
a  plant  of  20  metric  tons  capacity  in  10  hours  on  roasted  blende- 
pyrite  concentrate,  employing  the  Humboldt  separator. 

At  Peyrebrune,  Germany,  the  Peyrebrune  Co.  is  operating  a 
separating  plant  equipped  with  Humboldt  separators  on  blende- 

1  B.-,  H.-  und  S.-  Wesen,  vol.  xxv,  p.  474. 


THE   SEPARATION  OF  PYRITE  AND  BLENDE  135 

pyrite  concentrate;  the  capacity  of  the  plant  is  8  metric  tons  in  10 
hours. 

At  Kattowitz,  Germany,  there  is  a  magnetic  separation  plant 
equipped  with  twelve  Stern  wet-type  separators  treating  roasted 
blende-pyrite  ore  and  concentrate.  The  capacity  of  the  plant  is 
from  5  to  7.5  metric  tons  per  hour. 

At  Torrelavega,  Santander,  Spain,  the  Real  Compania  As- 
turiana  de  Minas  is  operating  a  magnetic  separation  plant  on 
blende-pyrite  concentrate. 

SEPARATION   OF   MAGNETIC   BLENDE   FROM   PYRITE 

At  The  Yak  Mill,  Leadville,  Colorado,1  International  sep- 
arators are  employed  to  separate  magnetic  blende.  The  ores 
treated  at  this  mill  carry  blende,  pyrite  and  pyrrhotite  and,  as 
nearly  as  can  be  learned,  carry  from  20  to  30  per  cent.  zinc.  The 
ore  is  treated  raw,  the  blende  being  recovered  as  a  magnetic 
product.  There  are  eighteen  of  these  machines  installed  here,  four 
of  which  receive  the  initial  ore ;  the  others  treat  the  products  of  the 
original  machines.  The  daily  capacity  of  the  mill  is  from  200  to 
250  tons,  making  the  amount  handled  by  the  primary  separators 
upward  of  50  tons  each.  The  capacity  of  one  of  these  machines  on 
20  per  cent,  ore  is  stated  at  2.5  tons  per  hour,  and  3  tons  per  hour 
on  30  per  cent.  ore.  The  ore  is  reduced  dry  to  pass  a  0.043-in. 
screen  aperture.  The  eighteen  machines  use  64  amperes  at  250 
volts  for  excitation,  or  less  than  1  kwt.  per  machine.  One  horse 
power  is  ample  for  the  mechanical  operation  of  the  separator.  No 
data  as  to  the  results  obtained  are  available.  Experiments  are  now 
being  carried  on  with  the  Cleveland-Knowles  separator,  the  ore  be- 
ing given  a  preliminary  roast. 

At  Denver,  Colorado,  the  Colorado  Zinc  Co.  is  treating  mag- 
netic blende  ores  on  Wetherill-Rowand  separators  and  Blake- 
Morscher  electrostatic  separators.  The  ores  treated  come  from 
Georgetown,  Black  Hawk,  Breckinridge,  and  Leadville,  and  carry 
magnetic  and  nonmagnetic  blende,  galena,  pyrite,  and  a  little  pyr- 
rhotite. The  ore  varies  in  size  down  to  classifier  products,  and 
carries  from  22  to  30  per  cent.  zinc. 

The  plant  is  equipped  with  three  Type  E  Wetherill-Kowand 

1  "Report  of  the  Zinc  Commission,  British  Columbia,"  p.  112. 


136  ELECTRO-MAGNETIC  ORE   SEPARATION 

separators  and  three  double  Blake-Morscher  electrostatic  separators, 
together  with  Wilfley  tables,  crushers,  rolls,  etc.,  for  the  prelim- 
inary concentration  of  such  raw  ores  as  are  purchased.  At  the 
time  of  the  writer's  visit  the  material  treated  by  the  separators  was 
the  middling  product  from  the  Wilfley  tables,  crushed  to  30  mesh 
before  concentration,  and  carrying  from  20  to  25  per  cent,  zinc 
with  25  to  28  per  cent,  iron  as  pyrite. 

The  middling  from  the  tables  is  raised  to  a  hopper  by  a  skip, 
and  fed  into  the  upper  end  of  a  cylindrical  drier  Devolving  on  an 
inclined  axis,  and  from  this  is  transferred  to  the  separator  bins, 
being  cooled  on  the  way. 

The  separators  are  standard  size,  18-in.  belt  with  six  separating 
zones,  operated  at  the  rate  of  17  tons  of  feed  per  machine  per  24 
hours,  which  appeared  to  be  somewhat  above  their  capacity,  which 
is  said  to  average  700  to  1000  Ibs.  per  hour,  at  which  rate  each 
machine  requires  7.5  H.P.  for  excitation  and  operation.  The  belt 
speeds  for  this  tonnage  were:  conveyor  belt,  45  ft.  per  minute; 
take-off  belts,  about  7  ft.  per  second;  feeder,  6  R.P.M.  The  cur- 
rent employed  on  the  several  magnets  could  not  be  ascertained. 
The  separators  make  four  products,  as  follows:  s. 

(1)  From  the  first  pole  of  the  first  magnet,  carrying  least  cur- 
rent, a  rather  strongly  magnetic  product  consisting  of  pjrrhotite, 
small  particles  of  pyrite  which  have  been  rendered  magnetic  in 
the  drying  furnace,  etc.     This  material  forms  tufts  or  bunches 
which  do  not  lose  their  magnetism  for  some  seconds  after  leaving 
the  magnets;  it  carries  from  7  to  11  per  cent,  zinc,  and  is  trammed 
to  the  waste  dump. 

(2)  From  the  second  pole  of  the  first  magnet,  a  light-colored 
product  carrying  from  12  to  15  per  cent,  zinc;  it  is  repassed. 

(3)  From  the  four  poles  of  the  second  and  third  magnets,  fin- 
ished zinc  concentrate  carrying  from  41  to  43  per  cent,  zinc  and 
10  to  12  per  cent,  iron;  the  iron  in  this  product  is  mostly  in  com- 
bination with  the  blende,  but  a  small  percentage  is  due  to  pyrite. 

(4)  Discharge  from  the  conveyor  belt,  consisting  of  pyrite  and 
nonmagnetic  blende,  and  carrying  from  10  to  14  per  cent,  zinc;  it 
is  sent  to  the  electrostatic  separators. 

The  zinc  content  of  the  products  from  the  several  poles  in- 
creases directly  with  the  current  employed  on  the  magnets;  is 
lowest  from  the  first  magnet,  which  receives  the  least  current  and 
highest  from  the  last,  which  receives  the  strongest  current,  and 


THE  SEPARATION  OF  PYRITE  AND  BLENDE  137 

which  apparently  removes  a  greater  quantity  of  product  than 
any  of  the  others. 

The  grade  of  the  tailing  product  depends  almost  entirely  upon 
the  condition  of  the  zinc  in  the  feed;  the  more  nonmagnetic  zinc 
there  is  in  the  feed  the  higher  the  zinc  content  of  this  product. 
The  tailing  also  carries  a  small  amount  of  feebly  magnetic  blende, 
which  would  be  taken  up  by  the  magnets  were  the  capacity  of  the 
separators  cut  down  and  the  speed  of  belt  travel  reduced. 

At  Canyon  City,  Colorado,  the  Empire  Zinc  Co.  is  operating  a 
plant  equipped  with  ten  Wetherill-Rowand  separators  and  one 
Wetherill  Type  F  separator,  on  magnetic-blende  ores. 

At  Ille  et  Vilaine,  France,  the  La  Touche  Mining  Co.  is  oper- 
ating a  plant  of  12  metric  tons  capacity  in  10  hours  on  magnetic 
blende  ores.  The  Humboldt- Wetherill  separator  is  employed. 

The  Societe  des  Mines  de  Balia  Karaidin,  Constantinople, 
Turkey,  is  operating  a  plant  of  4  metric  tons  hourly  capacity  on 
unroasted  blende-pyrite  ores.  The  Humboldt- Wetherill  separator 
is  employed. 

At  Minaca,  Chihuahua,  Mexico,  the  Calera  Mining  Co.  is  oper- 
ating Wetherill-Rowand  separators  for  the  recovery  of  blende  from 
the  tailing  from  an  ore  carrying  galena,  blende,  and  pyrite  in  a 
garnet  gangue,  which  is  concentrated  on  Sutton-Steele  pneumatic 
tables.  The  concentrate  obtained  carries  from  40  to  45  per  cent, 
zinc. 


VII 
THE    SEPARATION   OF    SIDERITE    FROM    BLENDE 

THE  specific  gravities  of  blende  (3.9  to  4.2)  and  siderite  (3.7 
to  3.9)  are  almost  identical,  and  they  may  not  be  separated  by  any 
method  based  on  this  property.  The  most  important  application 
of  magnetic  separation  in  Europe  has 'been  the  separation  of  sider- 
ite, or  carbonate  of  iron,  from  blende.  Many  important  ore  bodies 
carrying  galena  and  blende  have  siderite  as  their  chief  gangue  min- 
eral. The  method  followed  in  the  treatment  of  these  ores  consists 
of  the  removal  of  the  galena  by  water  concentration,  followed  by 
magnetic  separation  of  the  middling  products  containing  the 
blende  and  siderite.  Formerly  the  siderite  was  removed  after  cal- 
cination to  the  oxide,  but  since  the  advent  of  the  separators  with 
intense  magnetic  fields  direct  separation  of  the  raw  siderite  as  a 
magnetic  product  has  superseded  the  older  process.  Examples  of 
the  separation  of  siderite  after  calcination  are  given,  as  this 
method  possesses  advantages  over  the  direct  separation  in  the  treat- 
ment of  certain  ores.  Siderite  has  been  separated  magnetically 
after  calcination  for  its  value  as  iron  ore:  the  separation  of  sid- 
erite from  chalcopyrite  will  be  taken  up  in  a  later  chapter.  The 
magnetic  tailing  from  most  European  mills  finds  a  market  as  iron 
ore. 

Siderite,  sp.  gr.  3.7  to  3.9,  FeC03,  is  slightly  magnetic. 
Delesse  states  that  if  the  magnetic  permeability  of  steel  be  taken 
at  100,000,  that  of  siderite  is  120.  Crane  obtained  a  permeability 
for  a  specimen  from  Roxbury,  Conn.,  of  1.0234,  and  for  a  speci- 
men from  Allevard,  France,  of  1.0213.  Siderite  is  readily  trans- 
formed into  the  magnetic  oxide  of  iron  by  calcination. 

Ores  in  which  the  blende  is  in  part  magnetic,  or  the  siderite 
accompanied  by  pyrite,  should  be  roasted  before  separation.  Im- 
portant deposits  of  such  ores  are  found  in  British  Columbia,1  in 

1  "Report  of  the  Commission  Appointed  to  Investigate  the  Zinc  Resources 
of  British  Columbia."  W.  R.  Ingalls. 

138 


THE   SEPARATION   OF   SIDERITE  FROM   BLENDE         139 

the  treatment  of  which  magnetic  separation  would  seem  to  be  des- 
tined to  play  an  important  part. 

Ores  carrying  important  amounts  of  strongly  magnetic  blende, 
or  marmatite,  may  demand  treatment  in  two  stages:  preliminary 
separation  of  the  strongly  magnetic  blende  on  a  high-intensity  sep- 
arator, followed  by  roasting  and  separation  on  low-intensity  ma- 
chines. The  current  on  the  magnets  of  the  primary  separator  may 
be  regulated  to  remove  the  blende  down  to  a  point  where  its  per- 
meability approaches  that  of  siderite,  then  after  calcination,  the 
magnetic  oxide  may  be  removed  by  the  low-intensity  separators 
without  affecting  the  remaining  blende,  as  the  increase  in  perme- 
ability on  the  part  of  the  ferruginous  blende,  due  to  the  roast,  is 
slight  as  compared  with  the  difference  between  raw  siderite  and 
the  magnetic  oxide  into  which  it  is  transformed.  This  treatment, 
while  requiring  an  additional  separator,  has  the  advantage  of  pro- 
ducing two  clean  zinc  concentrates  which  may  be  marketed  sep- 
arately, the  first  product  removed  carrying  the  higher  percentage 
of  combined  iron,  and  therefore  being  of  lower  zinc  tenor. 

CALCINING  SIDERITE  TO  THE  MAGNETIC  OXIDE 

Siderite  heated  to  800°  C.  breaks  up  into  ferrous  oxide  and  cor- 
bonic  acid  gas.  If  the  roasting  is  carried  out  in  a  neutral  atmos- 
phere the  ferrous  oxide  is  transformed  into  the  ignition  oxide 
Fe607,  or,  if  the  atmosphere  is  moderately  oxidizing,  Fe304  re- 
sults; both  of  these  oxides  are  strongly  magnetic.  If,  however, 
there  is  free  access  of  air  the  nonmagnetic  Fe203  is  quickly  formed. 
The  whole  success  of  the  operation  lies  in  the  complete  control  of 
the  air  entering  the  furnace.  If  air  is  absent,  the  ferrous  oxide 
reacts  with  the  C02  with  the  formation  of  Fe304,  and  the  libera- 
tion of  carbon-monoxide;  this  reaction  does  not  take  place,  how- 
ever, unless  the  air  is  completely  excluded.  After  the  C02  is 
completely  driven  off,  it  is  very  easy  to  overroast  the  charge  to  the 
nonmagnetic  red  oxide,  but  if  the  operation  is  so  controlled  as  to 
leave  a  small  percentage  combined  the  tendency  to  overroast  is  much 
reduced,  without  appreciably  affecting  the  magnetic  qualities  of  the 
product.  Siderite,  when  pure,  contains  37.9  per  cent.  C02,  and  a 
large  loss  in  weight  results  from  the  calcination.  Siderite  is  usually 
mixed  with  from  3  to  5  per  cent,  of  fine  coal,  or  coke,  before  cal- 
cination, to  aid  in  its  decomposition  and  to  insure  a  reducing,  or 


140  ELECTRO-MAGNETIC  ORE   SEPARATION 

neutral,  atmosphere  in  the  furnace :  if  coal  is  used  it  must  be  of  a 
noncoking  variety.  In  the  treatment  of  ores  which  carry  both 
siderite  and  pyrite  a  roast  suitable  to  convert  the  carbonate  into 
the  oxide  also  suffices  to  transform  the  sulphide  into  the  magnetic 
sulphide,  in  which  state  it  is  removed  from  the  blende  by  the  sep- 
arators. 

The  calcined  siderite  is  always  very  strongly  magnetic,  which 
may  partially  be  due  to  the  reduction  of  a  small  amount  of  metal- 
lic iron  by  the  coal  mixed  with  the  charge.  The  roast  is  usually 
conducted  at  850°  C.,  at  which  temperature  but  15  minutes  is  re- 
quired for  the  production  of  magnetic  oxide.  The  duration  of  the 
roast  is  also  governed  by  the  size  of  the  particles  treated :  from  20 
to  35  minutes  is  usually  employed  with  fine  material.  Prolonged 
heating  at  the  temperature  of  calcination  affects  the  blende.  With 
a  properly  conducted  roast  of  normal  duration  the  blende  is  cov- 
ered by  a  white  film  due  to  incipient  oxidation,  which  does  not 
indicate  a  significant  loss. 

The  temperature  of  the  roast  must  be  carefully  regulated,  as 
the  ferrous  oxide  has  a  strong  tendency  to  slag  with  any  siliceous 
particles  of  waste  there  may  be  in  the  material  treated,  forming 
aggregates  of  the  several  minerals.  Calcination  gives  rise  to 
marked  decrepitation.  The  calcined  ore  is  classified  before  sep- 
aration. 

Many  types  of  shaft,  reverberatory  and  cylindrical  furnaces 
have  been  used  for  the  calcination  of  siderite;  almost  any 
furnace  in  which  the  access  of  air  may  be  completely  controlled  is 
suitable. 

SEPARATION   OF   EAW   SIDERITE 

At  Neurikirchen,  Siegerland,  Germany,  the  Lohmannsfeld  Co. 
is  operating  a  magnetic-separation  plant  on  raw  siderite-blende  ores. 
The  ores  treated  carry  galena  and  blende,  with  rarely  a  little 
chalcopyrite,  in  a  gangue  of  siderite  and  quartz;  occasional  ac- 
cessory gangue  minerals  are  calcite  and  barite.  The  siderite 
carries  a  varying  quantity  of  manganese,  which  sometimes  reaches 
12  per  cent.  The  blende  is  quite  diamagnetic. 

The  material  for  separation  consists  of  the  middle  products 
from  water  concentration,  by  which  process  the  galena  and  the  2  or 
3  per  cent,  of  quartzose  gangue  which  the  ore  carries  are  removed. 


THE   SEPARATION   OF   SIDERITE   FROM  BLENDE 


141 


These  middle  products  vary  in  size  from  1  to  10  mm.  and  carry 
from  15  to  22  per  cent.  zinc. 

The  plant,  which  comprises  six  Humboldt-Wetherill  separators, 


142 


ELECTRO-MAGNETIC  ORE  SEPARATION 


was  installed  under  a  guaranty  to  produce  a  blende  concentrate 
assaying  from  42  to  46  per  cent,  zinc,  and  a  tailing  product  car- 
rying not  more  than  1  to  3  per  cent,  zinc,  from  a  feed  crushed  to 


THE   SEPARATION  OF   SIDERITE   FROM   BLENDE        143 

pass  a  3-mm.  screen,  it  having  been  determined  that  these  ores 
free  their  component  minerals  at  that  size. 

The  wet  material  from  the  concentrator  is  dried  upon  two  end- 
less belts  which  transport  it  through  kilns  heated  by  waste  steam 
from  the  engines;  it  remains  in  the  kilns  from  25  to  30  minutes 
and  arrives  at  the  first  trommels  quite  dry. 

The  dried  ore  is  delivered  from  the  belts  to  a  trommel  with 
3-mm.  screens,  the  fines  are  thence  transported  by  elevator  to  the 


FIG.  65.  — TRANSVERSE  SECTION  OF  SEPARATION  WORKS,  NEUNKIRCHEN, 

GERMANY. 


classifying  trommels,  while  the  oversize  is  crushed  in  rolls  and  re- 
turned to  the  trommel.  Before  reaching  the  classifying  trommels 
the  ore  is  carried  upon  a  conveyor  belt  beneath  an  electromagnet 
which  attracts  and  removes  any  strongly  magnetic  particles  it  may 
contain. 

The  classifying  trommels  divide  the  ore  stream  into  the  follow- 
ing sizes,  which  are  fed  separately  to  the  separators:  through 
0.75  mm.,  from  0.75  to  1.4  mm.,  from  1.4  to  2.0  mm.,  from  2.0  to 
3.0  mm.  The  separators  are  six  in  number,  arranged  in  three 
series.  The  first  separator  of  each  series  is  a  two-pole  machine, 
while  the  second  is  of  the  three-pole  type.  The  magnets  of  the 
first  separator  take  12  amperes  at  65  volts  and  separate  a  clean  sid- 
erite  product;  the  belt  speed  on  these  separators  is  40  meters  per 
minute.  The  material  passing  unaffected  from  the  two-pole  sep- 


144 


ELECTRO-MAGNETIC  ORE   SEPARATION 


arator  is  re-treated  on  the  three-pole  machines.  Here  the  current 
is  5  amperes  on  the  first  magnet  and  8  on  the  second ;  two  middling 
products  carrying  blende  and  siderite  are  here  removed,  and  the 
stream  passing  off  the  separator  constitutes  a  finished  blende  concen- 
trate. The  belt  speed  on  the  three-pole  separators  is  25  meters  per 
minute.  The  plant  treats  from  3  to  3.5  metric  tons  of  crude  ore 


FIG.  66.  — TRANSVERSE  SECTION  OF  SEPARATION  WORKS,  NEUNKIRCHEN, 

GERMANY. 


per  hour.  The  crew  required  is  one  foreman,  five  boys,  one  engine- 
man,  and  one  stoker.  The  cost  of  treatment  (a  year's  average)  is 
1.40  marks  (33Jc.)  per  ton  of  crude  material;  no  amortization  is 
reckoned  in  this  figure.  The  plant  cost  about  100,000  marks.1 

At  Ems,  Germany,  the  Emser  Blei  &  Silberwerk  Gesellschaf  t 2 
has  been  employing  two  Humboldt-Wetherill  separators  on  blende- 
siderite  concentrate  since  1900.  These  machines  are  fitted  with 
280-mm.  belts  and  each  has  two  magnets.  The  feed  is  received 
from  the  concentration  mill  in  the  following  sizes,  which  are 

1  Iron  and  Coal  Trades  Review,  July  15,  1904. 

2  Communicated  by  the  company. 


THE   SEPARATION   OF   SIDERITE  FROM  BLENDE        145 

treated  separately  on  the  machines :  3  to  4  mm.,  2  to  3  mm.,  1  to 
2  mm.,  i  to  1  mm.,  and  two  classes  of  fines.  The  average  capacity 
of  each  machine  per  ten  hours  is,  of  the  coarser  sizes,  12  metric 
tons,  and  of  the  fines,  3.5  metric  tons.  The  average  material 
treated  of  all  sizes  is  6.25  metric  tons.  The  feed  carries  18.5 
per  cent,  zinc  and  the  finished  zinc  product  42.5  per  cent.;  the 
siderite  tailing  carries  2.4  per  cent.  zinc.  The  cost  of  separation 
foots  up  to  2.24  marks  (average  of  a  year's  run).  This  total, 
which  does  not  include  royalty  or  amortization  of  plant,  is  made 
up  as  follows : 


Marks 

Supervision                                                           .    . 

0  09 

Labor 

1  38 

Supplies,  including  the  coal  used  in  drying        

0  49 

Maintenance 

0  07 

Power  

0  03 

Miscellaneous          .        ....        ... 

0  18 

2.24 

The  separators  are  fed  from  bins  and  deliver  their  products 
into  cars.  The  current  used  on  the  magnets  is  from  8  to  9 
amperes  at  90  volts. 

At  Musen  bei  Creuzthal,  Germany,  the  Gewerkschaft  Grube 
Staalberg  is  operating  Humboldt-Wetherill  separators  on  blende- 
siderite  concentrate.  The  capacity  of  the  plant  is  1.23  metric 
tons  per  hour.  Two  men  and  two  boys  constitute  the  total  work- 
ing force.  The  cost  of  separation  varies  from  1.50  to  2.50  marks 
and  averages  2.20  marks  per  ton  of  feed.  This  figure  includes 
labor,  coal,  lubricants,  repairs,  and  supervision,  but  does  not  in- 
clude royalty. 

At  Lauenburg,  Germany,  The  Rheinische-Nassauische  Aktien- 
Gesellschaft  is  operating  a  plant  on  blende-siderite  ores,  employing 
the  Mechernich  separator.  The  ore,  pulverized  to  pass  a  screen 
with  4-mm.  openings,  is  dried  in  a  revolving  kiln,  with  the  ex- 
penditure of  1  Ib.  of  coal  per  15  Ibs.  moisture  evaporated.  The 
dry  ore  is  passed  through  a  dry-screening  apparatus  which  removes 
all  material  below  50  mesh.  The  coarse  product  is  passed  through 
a  trommel  with  2-mm.  and  J-min.  screens.  The  fines  are  treated 


146 


ELECTRO-MAGNETIC  ORE   SEPARATION 


in  a  dust  trommel,  and  everything  passing  120  mesh  is  removed. 
The  larger  sizes  are  separated  on  motortype  separators  and  the 
fines  on  the  Mechernich  separator.  The  machines  are  enclosed  in 
dust-tight  housings  and  the  dust  exhausted  by  fans. 


RESULTS  OF  SEPARATION 


Per  Cent. 
Zinc 

Per  Cent. 
Iron 

Feed  

19  5 

21   02 

Concentrate  

43  81 

5  47 

Middling 

7  9 

27  6 

Tailing  

2  6 

45  27 

The  average  recovery  of  zinc  in  the  concentrate  is  given  at 
85.72  per  cent,  of  the  total  zinc  in  the  feed. 

EUROPEAN    PLANTS    TREATING    RAW    SIDERITE    ORES 


NAME  OF  COMPANY 

Location 

Make  of  Separator 

Capacity, 
Metric 
Tons  per 
10  Hours 

Berzelius,  A.-G  

Bensberg,  Germany 
Friedrichssegen  
Neunkirchen  
Bendisberg 

Humboldt-Wetherill 
Humboldt-Wetherill 
Mechernich. 

30 

Gesellschaft  Friedrichssegen 
Gesellschaft  Peterszeche  
B.-G.  Bendisberg  

Humboldt-Wetherill 
Humbold^Wetherill 
Humboldt-Wetherill 
Humboldt-Wetherill 
Mechernich  

10 
10 
10 

50 

Victoria  Mining  Co       .    . 

Littfeld 

A.-G.  Vielle  Montagne 

Unter  Eschbach  
Marienhutte 

Bergamt  Marienhutte 

Gewerkschaf  t  Bliesenbach.  . 
Basterra  y  Hejos  

Bliesenbach  

Bilboa,  Spain  • 
Budel,  Spain  

Humboldt-Wetherill 
Humboldt-Wetherill 
Primosigh  .  .  . 

8 
6 

Ste.  des  Zincs  de  la  Campine, 
Ste.  Pertusola  

Genumari,  Italy.  .  . 

SEPARATION   OF    CALCINED   SIDERITE   FROM   BLENDE* 

Friedrichssegen,  Germany.  The  ore  from  the  Friedrichssegen 
mines  has  been  treated  by  magnetic  separation  for  some  25  years. 
Up  to  within  a  few  years  ago  the  method  followed  included  cal- 
cination and  separation  on  low-intensity  separators;  the  ores  are 


THE   SEPARATION   OF   SIDERITE  FROM   BLENDE        147 


now  separated  direct  on  Humboldt-Wetherill  machines.  The  de- 
scription of  the  old  process  is  included,  as  it  is  a  standard  method 
for  the  treatment  of  blende-siderite  ores,  the  direct  separation  of 
which  is  not  always  advisable. 


148 


ELECTRO-MAGNETIC  ORE   SEPARATION 


The  ore  treated  at  Friedrichssegen  was  a  mill  product,  assay- 
ing from  11  to  15  per  cent,  zinc  (as  blende)  and  18  to  23  per 
cent,  iron  (as  siderite).  This  was  heated  to  redness  in  a  furnace 
of  the  McDougal  type,  which  put  through  from  20  to  25  metric 
tons  per  24  hours,  according  to  the  size  of  particles;  the  coal 
consumption  was  1.2  metric  tons.  The  plant  comprised  two  fur- 
naces, each  of  which  required  the  attention  of  one  man,  who  also 
trammed  the  calcined  ore  to  the  cooling  floor.  When  the  ore  had 
cooled  to  50°  C.,  or  lower,  it  was  elevated  to  a  trommel  which  di- 


Middllngs 

FIG.  68.  — ARRANGEMENT  OF  SEPARATORS,  FRIEDRICHSSEGEN,  GERMANY. 

vided  it  into  sizes  as  follows :  over  4  mm. ;  between  2  and  4  mm. ; 
and  through  2  mm.  The  material  which  was  refused  by  a  4-mm. 
screen  was  sent  to  a  set  of  rolls  and  reduced  to  4-mm.  and  elevated 
again  to  the  trommel.  The  two  sizes  passing  the  screens  dropped 
into  separate  bins  from  which  they  were  fed  to  the  primary  sep- 
arators. There  were  twelve  primary  separators,  arranged  in  three 
groups  of  four  each;  the  four  machines  of  each  group  were  set 
up  in  pairs,  tandem.  The  arrangement  of  the  separators  in  each 
group  is  shown  in  the  above  figure.  The  ore  diverted  to  a  group 
was  divided  equally  between  machines  A  and  5,  which  made  two 
products,  one  enriched  in  zinc  and  one  enriched  in  iron.  The  iron 
product  of  both  machines  was  led  to  D  and  the  zinc  product  to 
(7.  The  two  lower  machines  made  a  zinc  product  with  38  to  42  per 
cent,  zinc  and  6  per  cent,  iron  at  the  most,  a  mixed  product,  and 
an  iron  product  which  still  retained  6  to  8  per  cent.  zinc.  The 
mixed  product  was  re-treated  by  a  group  of  two  machines  and  the 
iron  product  by  another  group  of  four  machines,  which  yielded  a 


THE   SEPARATION   OF    SIDERITE   FROM   BLENDE         149 


finished  iron  product  containing  40  per  cent,  iron  and  3  to  4  per 
cent,  zinc,  representing  the  entire  loss  of  the  process.  Out  of  a 
total  of  eighteen  separators,  twelve  were  employed  on  original  ore, 
while  six  were  used  cleaning  the  products  of  the  primary  machines  ; 
the  general  arrangement  of  the  plant  is  shown  in  the  accompanying 
figure.1 

At  Maiern,  Austria,  there  is  a  magnetic  separation  mill  sep- 
arating siderite  from  blende  after  calcination. 

FLOW  SHEET  OF  MAGNETIC  SEPARATION  PLANT,  MAIERN, 

AUSTRIA 

ition 


Calcinat 


Screening 


3  mm.  Size  2  mm.  Size 

Magnetic  Separator  I 


I  mm.  Size  0.5  mm.  Size 

Magnetic  Separator  II 


Blende 


Blende 


lion  Ore 


'  Becrushing  liolls 

J 

Screening 

, i k 

r~  ~i 

1  mm.  Size  Dust 

Magnetic  Separator  III 


Blende 


Magnetic  Separator  IV 


Iron  Ore 


Beworked  alone  on  Separator  IH 


Blende  Iron  Ore 


Iron  Ore  Blende 


Beworked  alone  on  Separator  IV 


Iron  Ore  Blende 


Washed  on  Table 


Blende  Gangue 

The  ore,  after  calcination,  is  crushed  to  pass  4  mm.  and  then 

classified  into  the  following  sizes :  on  3  mm. ;  on  2  mm. ;  on  1  mm. ; 

and  through  £  mm.     The  two  larger  sizes  are  treated  upon  Sep- 

1  Report  of  the  Zinc  Commission,  British  Columbia,"  W.  R.  Ingalls,  p.  85. 


150  ELECTRO-MAGNETIC  ORE   SEPARATION 

arator  No.  1,  and  the  smaller  on  Separator  No.  2.  These  separa- 
tors make  clean  blende  and  a  middling  product  taken  out  by  the 
magnets.  The  middling  from  Separator  No.  1  is  recrushed  and 
classified  upon  a  1-mm.  screen;  the  sand  and  finer  sizes  from  this 
classification  are  treated  at  different  times  upon  Separator  No.  3, 
which  produces  a  clean  iron  product  and  a  blende  product  which  is 
subjected  to  a  repassage  over  the  same  machine;  the  products 
from  this  second  passage  are  a  clean  blende  and  a  finished  iron 
product.  The  middling  from  Separator  No.  2  is  passed  over 
Separator  No.  4;  from  this  a  clean  iron  product  is  obtained  and  a 
zinc  product  which  is  repassed  over  the  same  machine,  giving  on 
the  second  pass  a  finished  iron  product  and  a  zinc  product  which  is 
cleaned  by  tables.1 

Heberle  separators  ...are  employed,  the  capacity  on  the  two 
coarser  sizes  being  1J  tons  per  hour,  and  of  the  fines,  1  ton  per 
hour.  The  speed  at  which  these  separators  may  be  operated  is  lim- 
ited, owing  to  the  fact  that  beyond  a  certain  point  centrifugal 
force  is  sufficient  to  overcome  the  magnetism  and  throw  off  mag- 
netic particles ;  this  limiting  speed  is,  for  the  60-cm.  drum,  45 
R.P.M.2 

At  Allevard,3  France,  there  is  an  installation  for  calcining  and 
magnetic  separation  of  siderite  for  its  value  as  an  iron  ore.  The 
ore  consists  of  siderite  in  a  gangue  of  sandstone,  slate,  and  quartz. 
The  raw  ores  are  screened  on  a  grizzly  with  bars  spaced  1£  ins. 
The  coarse  ore  is  hand  picked,  the  waste  thrown  out,  and  the  bal- 
ance calcined  in  shaft  furnaces.  After  calcination  the  lumps  are 
broken  up  and  the  pieces  of  waste  which  have  not  been  rendered 
friable  in  the  furnaces  are  thrown  out.  The  coarse  ore  is  not  sub- 
jected to  magnetic  separation.  The  final  product  from  this  mate- 
rial carries  in  excess  of  50  per  cent,  iron  and  manganese.  The 
fines  are  screened,  and  material  passing  -^  in.  is  sent  directly  to 
shelf-calcining  furnaces,  the  material  between  -fa  and  1£  ins.  is 
sized  and  jigged  and  the  concentrate  calcined  in  reverbatory  fur- 
naces and  separated.  The  calcining  is  conducted  at  a  temperature 
of  1000°  C.  The  loss  of  weight  in  the  furnaces  is  28  per  cent., 
and  the  calcined  charge  still  retains  2  per  cent.  C02.  The  sep- 

.     '  "La  Separation  Electromagnetique  et  Electrostatique,"  D.  Korda,  p.  127. 

2  Richards's  "Ore  Dressing,"  p.  798. 

»M.  G.  Gromier,  "Bull,  de  la  Societe"  de  Tlndustrie  Mineral,"  Series  III, 
vol.  vii,  p.  465. 


THE  SEPARATION  OF   SIDERITE  FROM  BLENDE         151 

arators  used  consist  of  wooden  drums  upon  which  a  number  of 
small  magnets  are  mounted.  The  fines,  after  separation,  are  bri- 
quetted  after  addition  of  5  per  cent,  slaked  lime.  The  capacity 
of  the  plant  is  from  210  to  220  metric  tons  in  10  hours. 

At  Krompach,  Austria?  the  Hernadthal  Ungarische  Eisenin- 
dustrie  Aktien-Gesellschaft  has  been  operating  a  magnetic-separat- 
ing plant  of  10  metric  tons  daily  capacity  since  1901.  This  plant 
was  installed  to  try  out  a  method  for  treating  the  Szlovinka  ore 
bodies,  and  has  also  been  operated  as  a  custom  plant.  On  the 
basis  of  the  results  obtained  a  mill  of  500  metric  tons  daily  capac- 
ity is  now  being  built. 

The  Szlovinka  ores  consist  of  siderite  occurring  with  quartz 
and  schist,  and  lesser  amounts  of  finely  divided  chalcopyrite,  py- 
rite,  and  tetrahedrite ;  the  latter  mineral  occurs  finely  disseminated. 
The  high  copper  and  sulphur  content  has  hitherto  rendered  this 
class  of  ore  unworkable,  and  the  object  of  the  enterprise  is  to  pro- 
duce a  commercial  iron  concentrate  through  the  elimination  of 
these  impurities,  while  also  obtaining  a  marketable  copper  con- 
centrate as  a  by-product. 

The  run  of  mine  ore  after  hand  picking  is  crushed  to  2.5  mm. 
in  breakers  and  rolls,  and  is  then  passed  through  a  revolving  dryer 
before  classification.  The  dry  ore  is  next  divided  by  shaking-screens 
into  the  following  sizes:  2.5  mm.  to  2  mm.,  2  mm.  to  1.5  mm., 
1.5  mm.  to  1  mm.,  1  mm.  to  0.5  mm.,  0.5  mm.  to  0.25  mm.  and 
through  0.25  mm.  The  coarser  sizes  from  2.5  mm.  down  to 
0.25  mm.  are  treated  separately  on  24  Primosigh  dry  separators, 
while  the  material  passing  0.25  mm.  is  treated  on  four  wet  sep- 
arators of  the  same  make. 

The  magnetic  product  from  these  machines  is  sent  to  a  battery 
of  revolving  furnaces  where  it  is  calcined  and  sintered,  removing 
all  but  traces  of  sulphur,  and  preparing  the  product  for  the  iron 
furnaces.  The  middling  product  from  the  dry  separators  is  re- 
crushed  dry  in  a  ball  mill  to  0.25  mm.  and  fed  to  the  wet  sep- 
arators; it  amounts  to  less  than  one  half  on  one  per  cent,  of  the 
feed.  The  nonmagnetic  product  from  the  dry  separators  is  con- 
centrated on  tables  which  deliver  a  copper  concentrate  and  tail- 
ing; the  nonmagnetic  product  from  the  wet  separators  is  similarly 
treated  after  dewatering  and  classification  in  spitzkasten,  etc. 

J  Communicated  by  the  Marchegger  Maschinenfabrik  und  Eisengiesserei, 
Marchegg  bei  Wien,  Austria. 


152  ELECTRO-MAGNETIC  ORE   SEPARATION 


ANALYSIS  OF   PRODUCTS 

Raw  ore 27.37  %  Fe     0.911  %  Cu     1.511  %  S. 

Magnetic  concentrate 33.5    %  Fe     0.17    %  Cu     (70  %  of  feed). 

Same  after  sintering 50       %  Fe     0.23    %  Cu  and  trace  S. 

The  low  iron  content  of  the  magnetic  concentrate  is  due  to 
the  fact  that  the  siderite  is  contaminated  by  magnesia. 

The  separators  are  fed  and  their  products  removed  by  a  system 
of  belt  conveyors,  thus  avoiding  manual  labor  and  rendering  the 
passage  of  the  ore  through  the  mill  automatic. 


VIII 

SEPARATION    OF   MISCELLANEOUS    ORES   AND 
MINERALS 

SEPARATION  OF  COPPER-IRON  SULPHIDES 

Chalcopyrite,  sp.  gr.  4.15  to  4.3,  is  too  feebly  magnetic  to  be 
separated  raw,  and  must  be  roasted  to  either  the  magnetic  sulphide 
or  the  magnetic  oxide,  these  changes  taking  place  in  a  manner  sim- 
ilar to  the  behavior  of  pyrite.  A  one-minute  roast  at  a  red  heat  is 
sufficient  to  impart  magnetism  to  chalcopyrite  through  the  forma- 
tion of  the  magnetic  sulphide ;  the  magnetic  oxide  requires  a  longer 
roast  for  its  formation.  Both  of  these  compounds  are  very 
strongly  magnetic.  Chalcopyrite  is  extensively  concentrated  by 
magnetism  in  Europe,  and  the  application  is  growing.  This  is 
due  to  the  fact  that  chalcopyrite  slimes  readily  on  crushing,  re- 
sulting in  a  low-percentage  recovery  by  water  concentration.  The 
fine,  strongly  magnetic  particles  of  chalcopyrite  are  easily  saved  by 
magnetic  separation  in  a  product  representing  a  high  ratio  of 
concentration.  The  separation  of  chalcopyrite  from  garnet  (sp. 
gr.  3.1  to  4.3)  and  epidote  (sp.  gr.  3.25  to  3.5)  and  other  heavy 
gangue  minerals  constitutes  a  further  important  application  of 
magnetic  separation,  these  silicates  being  feebly  magnetic  as  com- 
pared with  roasted  chalcopyrite. 

Cupriferous  Pyrites.  —  Cupriferous  pyritic  ores  have  been  the 
subject  of  numerous  tests  which  indicate  a  good  percentage  re- 
covery from  even  very  low-grade  material.  Except  in  special  in- 
stances, however,  such  ores  may  be  more  cheaply  treated  by  other 
methods,  and  the  writer  is  not  informed  of  any  installation  in 
operation  upon  them. 

At  Corinth,  Vermont,1  the  Pike  Hills  Mines  Co.  is  employing 
the  Wetherill-Rowand  separator  in  separating  pyrrhotite  and  chal- 
copyrite from  gangue  and  from  each  other.     The  ore  carries  pyr- 
1  Communicated  by  Mr.  H.  G.  Hunter,  Supt. 
153 


154  ELECTRO-MAGNETIC  ORE   SEPARATION 

rhotite  and  chalcopyrite  in  a  quartz  and  mica  schist  gangue;  the 
run  of  mine  ore  is  cobbed  to  run  3  per  cent,  copper  before  going  to 
the  mill.  The  cobbed  ore  is  dry-crushed  through  10 -mesh,  and 
screened  into  two  sizes,  through  20  mesh,  and  through  10  on  20 
mesh.  The  two  sizes  are  run  separately  through  the  separators  as 
they  require  different  adjustments  in  the  height  of  magnets  and 
intensity  of  the  field.  The  crushed  ore  is  fed  to  a  Wetherill-Row- 
and  separator,  which  .removes  the  pyrrhotite ;  the  pyrrhotite  carries 
0.5  per  cent,  copper,  and  is  stacked  for  future  use  in  smelting  sili- 
cious  ores.  The  residue  passing  from  the  separator,  consisting  of 
chalcopyrite  and  gangue,  is  passed  through  a  revolving-cylinder 
furnace,  and  given  a  slight  roast,  sufficient  to  form  a  film  of  mag- 
netic sulphide  on  the  chalcopyrite  particles.  The  ore  passing  from 
the  furnace  is  cooled  and  fed  to  a  second  Wetherill-Rowand  sep- 
arator which  removes  the  chalcopyrite  as  a  magnetic  product;  the 
concentrate  from  this  machine  carries  from  12  to  20  per  cent, 
copper,  and  the  tailing  from  0.2  to  0.5  per  cent,  copper,  varying 
with  the  quality  of  the  ore  and  the  amount  put  through. 

At  Fredricktown,  Missouri,  the  North  American  Lead  Co.  is 
operating  four .  Dings  separators  on  copper,  iron,  and  nickel  sul- 
phides. The  ore  is  roasted  in  a  McDougal  furnace.  The  roasted 
chalcopyrite  is  removed  by  the  first  magnet  of  the  separator,  and 
this  product  is  smelted  directly  to  black  copper.  The  product 
from  the  second  magnet  carries  cobalt  and  nickel,  and  is  treated 
electrolytically.  The  percentage  saving  of  copper  is  said  to  be  high, 
and  the  separation  efficient.  The  management  is  unwilling  to 
make  public  the  details  of  the  process. 

At  Ain-Barbar,  Algeria*  there  are  magnetic-separation  works 
treating  chalcopyrite-blende  ores. 

The  mines  at  Ain-Barbar  have  been  worked  for  many  years  for 
the  copper  values  of  their  ores.  These  ores  also  carry  blende,  and 
it  was  for  the  separation  of  this  mineral  from  the  copper  concen- 
trates that  the  magnetic  plant  was  installed.  The  ores  average  5 
per  cent,  copper  and  12  per  cent.  zinc.  A  preliminary  concentra- 
tion (hand  picking  and  jigging)  raises  the  grade  of  the  material 
destined  for  magnetic  treatment  to  12  per  cent,  copper  and  28  per 
cent.  zinc.  About  25  metric  tons  of  this  concentrate  are  produced 
daily. 

1  "La  Separation  Electromagnetique  et  Electrostatique,"  D.  Korda,  pp. 
114-119. 


SEPARATION  OF   MISCELLANEOUS  ORES  AND  MINERALS     155 


The  plant  is  equipped  with  a  cylindrical  roasting  furnace,  two 
Humboldt-Wetherill  separators  of  four  poles  each,  which  treat  the 
coarser  sizes,  and  one  double-pole  Mechernich  separator  for  the 
treatment  of  the  finer  sizes.  The  capacity  of  the  Wetherill  ma- 
chines is  8  metric  tons  in  10  hours. 

The  ore  is  given  a  preliminary  roast  and  classified  into  four 
sizes.  One  Humboldt-Wetherill  treats  two  sizes  above  1  mm.  and 
the  other  two  sizes  below  1  mm.,  the  dust  going  to  the  Mechernich. 

While  it  is  not  definitely  so  stated  in  the  description  of  this 
plant  by  the  engineer  in  charge  (M.  D.  Korda),  it  is  inferred  that 
the  actual  working  results  are  along  the  lines  of  those  obtained  on 
large-scale  tests  made  in  Germany  on  concentrate  shipped  from 
Algeria.  These  results  follow: 

TEST  ON  MECHERNICH  SEPARATOR 


Weight 
kilo- 

grammes 

Per  cent. 
Copper 

Per  cent. 
Zinc 

Per  cent. 
Iron 

Feed     

2,825 

5  4 

23  0 

15  8 

(Copper  concentrate 

861 

13  5 

8  16 

33  5 

Middling.        

123 

12  05 

14  05 

22  21 

Cleaned  blende 

1  841 

1  78 

40  55 

12  87 

The  feed  was  classified  into  the  following  sizes  before  separa- 
tion :  4  mm.-2  mm.,  2  mm.-J  mm.,  J  mm.-^j.  mm.,  and  dust.  The 
separate  products  afterwards  were  combined  under  the  names  given 
in  the  above  table. 

TEST  ON  HUMBOLDT-WETHERILL  SEPARATOR 


Weight 
kilo- 
grammes 

Per  cent. 
Copper 

Per  cent. 
Zinc 

Feed  

80.00 

6.7 

25.4 

8  4 

28.2 

No.  1  concentrate       

24  82 

18  57 

8  49 

No.  2  concentrate  

8.20 

11.5 

13.60 

Middling  ,  

5  39 

5  65 

23  38 

Nonmagnetic  product  

41.63 

1.95 

41.05 

156 


ELECTRO-MAGNETIC  ORE   SEPARATION 


A  farther  test  on  15  metric  tons  sensibly  confirmed  the  results 
on  the  above  preliminary  test. 

At  Yerington,  Nevada,  the  Bhiestone  Mining  &  Smelting  Co.  is 
operating  an  experimental  plant  on  an  ore  carrying  chalcopyrite  in 
an  epidote  and  garnet  gangue.  The  ore  is  crushed  to  8  mesh  and 
given  a  slight  roast  in  a  tower-roasting  furnace  and  passed  over  a 
Wetherill-Rowand  separator.  The  concentrate  obtained  carries  15 
per  cent,  copper. 

RESULTS  or  A  TEST  ON  A  CHALCOPYRITE-GARNET  ORE  x 

The  ore  for  the  test  carried  2.33  per  cent,  copper,  present  as 
chalcopyrite,  in  a  gangue  of  lime-alumina  garnet.  The  ore  was 
crushed  to  pass  10  mesh,  roasted,  and  passed  over  a  Wetherill-Row- 
and separator  excited  by  2.5  amperes.  The  results  follow: 


Per  cent, 
of  Feed 

Per  cent. 
Copper 

First  belt  concentrate  

9  3 

17.6 

Second  belt  concentrate                    

7.2 

6  0 

Nonmagnetic  tailing  

83.5 

0.25 

The  ratio  of  concentration  was  approximately  6  into  1,  and  the 
saving  88.5  per  cent,  in  the  combined  concentrates  assaying  12.5 
per  cent.  On  other  tests  savings  as  high  as  96  per  cent,  were  re- 
corded and  repeated  results  obtained  between  these  two  limits. 

MAGNETIC  SEPARATION  PLANTS  TREATING  CHALCOPYRITE 
ORES  ON  THE  HUMBOLDT-WETHERILL  SEPARATOR 


COMPANY 

Location 

Hourly 
capacity 
Metric  Tons 

Mitterberger  Kupfer-Gewerkschaft  
Mazzurana  Company                 

Innsbruck,  Austria  .  .  . 
Predazzo  

1.0 

0  4 

Caucasus  Copper  Company 

Caucasia,  Russia 

40  0 

Cerre  Muriano  Mines  Company      

Cordova,  Spain  

4.0 

Aramo  Copper  Mines 

Pola  de  Lena,  Spain 

1  5 

Oresund  Chemical  Works  

Stockholm,  Sweden  .  . 

1.0 

Hill  &  Stewart      .             

London,  England    .  .  . 

1.2 

Schuctermann  &  Kremer 

Dortmund  Germany 

1  Communicated  by  Mr.  John  B.  Keating,  Bully  Hill,  California. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     157 

At  San  Pedro,  New  Mexico,  the  Santa  Fe  Gold  and  Copper 
Company  is  constructing  a  magnetic-separation  plant  equipped 
with  roasting  furnace  and  Wetherill-Rowand  separators  to  treat 
an  ore  carrying  chalcopyrite  in  a  garnet  gangue.  Tests  have  indi- 
cated an  80  per  cent,  recovery  with  the  production  of  a  concentrate 
carrying  15  per  cent,  copper. 

SEPARATION    OF    COPPER    CARBONATES 

The  carbonates  of  copper,  sp.  gr.  3.5  to  4.0,  are  feebly  mag- 
netic: attempts  made  to  separate  them  from  their  gangues  com- 
mercially have  not,  however,  been  successful.  The  following  results 
are  reported  as  having  been  obtained  on  an  ore  carrying  malachite 
and  azurite  in  a  dolomitic  gangue.1  The  ore  contained  2.9  per 
cent,  copper,  and  was  passed  over  a  Humboldt-Wetherill  separator 
excited  by  18  amperes  at  90  volts,  and  fepassed  at  14  amperes. 
Of  the  total  feed,  12.6  per  cent,  was  recovered  as  a  concentrate  as- 
saying 17.2  per  cent,  copper,  and  85.4  per  cent,  of  the  total  feed 
as  tailing  assaying  0.75  per  cent,  copper,  indicating  an  extraction 
of  75.5  per  cent. 

SEPARATION   or    GARNET 

Most  varieties  of  garnet,  sp.  gr.  3.1  to  4.3,  are  sufficiently  mag- 
netic to  be  capable  of  separation  in  high-intensity  magnetic  fields. 
Garnet  is  separated  as  a  magnetic  product  at  Franklin  Furnace, 
N.  J.,  and  at  Broken  Hill,  N.  S.  W.  It  has  been  proposed  to  re- 
move garnet  magnetically  from  garnetiferous  schists  for  use  as  an 
abrasive.  An  application  which  is  likely  to  become  of  importance 
is  the  removal  of  garnet  from  copper  ore  and  concentrate,  garnet 
and  chalcopyrite  together  being  of  common  occurrence  in  contact 
metamorphic  deposits.  The  high  specific  gravity  of  the  garnet  and 
the  tendency  on  the  part  of  the  chalcopyrite  to  slime,  and  so 
cause  loss  in  concentration,  often  prevent  recourse  to  specific-grav- 
ity methods. 

SEPARATION   OF   PYRRHOTITE 

Pyrrhotite,  sp.  gr.  4.5  to  4.65,  is  in  most  specimens  strongly 
magnetic,  but  from  some  localities,  as  South  Strafford,  Vt.,  and 

1  "La  Separation  Electromagnetique  et  Electrostatique,"  D.  Korda,  p.  134. 


158  ELECTRO-MAGNETIC  ORE   SEPARATION 


certain  places  in  Virginia,  it  is  too  feebly  magnetic  to  be  affected 
by  intense  magnetic  fields.  Crane  gives  the  permeability  of  pyr- 
rhotite  from  the  Stobie  Mine,  Sudbury,  Ontario,  as  1.0782,  and  of 
a  specimen  from  the  Gap  Mine,  Lancaster  Co.,  Penn.,  as  1.0775. 
Pyrrhotite  is  separated  raw  as  a  magnetic  product  at  Corinth,  Vt., 
at  Broken  Hill,  N".  S.  W.,  and  in  Sweden.  The  feebly  magnetic  or 
nonmagnetic  varieties  of  pyrrhotite  become  strongly  magnetic  on 
being  subjected  to  a  slight  roast  at  a  low  heat ;  only  sufficient  heat 
to  cause  a  superficial  tarnish  appears  to  be  necessary.  This  pro- 
cedure was  followed  in  the  treatment  of  pyrrhotite-chalcopyrite 
ore  at  South  Stratford,  Vt. 

Numerous  experiments  have  been  carried  out  in  the  attempt 
to  separate  pentlandite,  a  compound  of  nickel,  from  pyrrhotite, 
with  which  mineral  it  is  frequently  associated,  notably  at  Sudbury, 
Ontario.  This  method  is  successful  in  the  treatment  of  clean  par- 
ticles, but  is  not  applied  commercially,  as  in  most  ores  the  pyrrho- 
tite, even  when  finely  comminuted,  carries  sufficient  pentlandite  to 
give  rise  to  a  prohibitive  loss  in  the  magnetic  tailing. 

At  Saxburget,  Sweden?  there  is  an  installation  employing  a 
Herbele  separator  to  remove  pyrrhotite  and  magnetite  from  a  lead- 
zinc  sulphide  ore.  The  ore  assays  11  per  cent,  lead  (as  galena),  22 
per  cent,  zinc  (as  blende)  with  14  per  cent,  magnetite,  2  to  5  per 
cent,  pyrrhotite  and  15  to  20  per  cent,  quartz.  The  mill  flo'w  sheet 
follows : 

Hand-picked  ore 


rush* 
levai 
f-in.  trommel 


Blake  crusher  to  £  in. 
elevator 


through  , 

oversize  oversize 

fine  rolls  coarse  rolls 


trommel 

through 

Herbele  separator 


[magnetic]  [nonmagnetic]  slime 

i  H.  C.  McNeill,  Jour.  Iron  and  Steel  Inst.,  August,  1899. 


SEPARATION  OF   MISCELLANEOUS  ORES  AND  MINERALS     159 

The  magnetic  product  contains  the  magnetite  and  pyrrhotite 
and  but  little  galena  and  blende.  The  nonmagnetic  product  of 
the  separator  is  concentrated  on  jigs,  tables,  etc.,  and  the  quartz 
removed.  The  overflow  from  the  separator  is  allowed  to  settle  and 
the  slime,  consisting  mostly  of  blende  and  silica,  is  treated  for  zinc. 

At  The  Pinnacles  Mine,  Broken  Hill,  N.  S.  W.,  tailing  from 
water  concentration  carrying  argentiferous  pyrrhotite  associated 
with  garnet  and  quartz  is  treated  on  an  Odling  separator.  The 
pyrrhotite  is  removed  raw  as  a  magnetic  product,  leaving  the  gar- 
net and  quartz  as  a  nonmagnetic  tailing. 

SEPARATION  OF  LIMONITE 

Limonite  frequently  accompanies  cerusite,  calamine,  and  smith- 
sonite,  all  being  the  products  of  oxidation  of  iron,  lead,  and 
zinc  sulphides.  Cerusite  may  be  separated  from  the  other  min- 
erals of  such  a  mixture  by  concentration,  but  the  specific  gravities 
of  the  limonite  and  the  zinc  minerals  are  too  similar  to  permit  of 
separation  by  any  method  depending  upon  specific  gravity. 

Limonite,  sp.  gr.  3.6  to  4.0,  is  feebly  magnetic;  Crane  gives 
1.0099  as  the  permeability  of  a  specimen  from  Nova  Scotia  and 
1.0098  for  a  specimen  from  Pennsylvania.  Calamine  has  a  specific 
gravity  of  from  3.16  to  3.49,  while  smithsonite  varies  from  4.3  to 
4.45.  Limonite  may  be  rendered  strongly  magnetic  by  roasting, 
to  which  it  is  usually  subjected  before  separation,  although  the 
mineral  has  been  commercially  separated  raw. 

CALCINING   LIMONITE   FOR   MAGNETISM 

Limonite  is  composed  of  2  parts  Fe203  and  3  parts  water; 
upon  heating  this  water,  which  amounts  to  14.4  per  cent.,  is  driven 
off,  leaving  the  nonmagnetic  sesquioxide,  which  must  be  reduced 
to  the  magnetic  Fe304  before  being  capable  of  separation.  The 
expulsion  of  the  water  leaves  the  mineral  porous,  and  therefore 
susceptible  to  the  action  of  the  furnace  gases.  The  roasting  may 
be  done  in  two  ways,  by  heating  at  a  comparatively  low  tempera- 
ture in  the  presence  of  reducing  gases,  or  by  heating  strongly  in 
the  absence  of  air,  by  which  process  one  atom  of  oxygen  is  driven 
off.  The  former  method  is  the  one  in  commercial  use,  as,  if  the 
ore  treated  contains  any  silica,  a  slag  is  easily  formed  at  the 


160 


ELECTRO-MAGNETIC  ORE  SEPARATION 


temperature  necessary  to  drive  off  the  oxygen.  At  Monteponi  the 
ore  is  mixed  with  2  per  cent,  fine  coal  and  calcined  for  6  hours 
in  revolving  cylindrical  furnaces;  200  kgm.  of  lignite  is  consumed 
in  the  fire  box  per  metric  ton  of  ore  treated.  At  Mercadel,  Spain, 
the  ore  is  mixed  with  from  1  to  5  per  cent,  of  fine  coal,  according 
to  the  amount  of  iron  present  in  the  ore,  and  ore  above  14  mm.  is 
roasted  in  shaft  furnaces  while  the  finer  material  is  roasted  in  re- 
verberatories.  At  Austin  ville,  Vav  the  ore  was  mixed  with  10  per 


FIG.    69A.  — CALAMINE    DRESSING    PLANT,    MONTEPONI,    SARDINIA. 


cent,  coal  and  roasted  in  reverberatory  furnaces  7  X  9  ft.  with 
20  X  84-in.  fire  boxes.  The  ore  remained  in  the  furnaces  2  hours, 
1  hour  being  required  to  bring  the  charge  up  to  a  red  heat,  and  1 
hour  at  this  heat  to  magnetize ;  the  furnace  charge  was  6  tons.  Ex- 
periments conducted  on  limonite,  in  which  it  was  heated  to  bright 
redness  and  producer  gas  passed  over  it,  gave  good  results. 

At  Monteponi,  Sardinia*  there  are  extensive  magnetic  separa- 
tion works  separating  limonite  from  oxidized  zinc  minerals.  The 
valuable  minerals  are  calamine,  smithsonite,  galena,  and  cerussite; 
the  lead  minerals  are  in  subordinate  amount.  The  gangue  is  princi- 

»  "Oestr.  Zeit.  fur  B.  und  H.-Wesen,"  vol.  xl,  pp.  233  and  347,  E.  Ferraris; 
and  communicated  by  E.  Ferraris. 


SEPARATION  OF  MISCELLANEOUS  ORES  AND  MINERALS     161 


pally  limonite  and  dolomitic  limestone,  but  it  also  carries  a  little 
barite. 

The  lead  minerals  are  separated  by  concentration  when  the 
light    gangue    is    also    eliminated;    the    middling    product,    or 


162 


ELECTRO-MAGNETIC  ORE   SEPARATION 


zinc  concentrate,  forms  the  bulk  of  the  material  for  magnetic 
separation,  carrying  besides  the  zinc  minerals,  limonite  and  zincy 
dolomite. 

There  are  three  magnetic-separation  plants  at  Monteponi,  two 


FIG.   69C.  — SHOWING  OPEN   CONSTRUCTION   OF   MILL,   MONTEPONI. 

of  them  employing  the  cross-belt  separators,  and  the  third  the 
drum  separator  respectively — the  Ferraris  Nos.  II  and  III  sep- 
arators. 


PLANTS   EMPLOYING   THE   FERRARIS   CROSS-BELT 
SEPARATORS 

The  raw  material  for  separation,  crushed  to  pass  a  6-mm. 
screen,  is  mixed  with  from  2  to  3  per  cent,  of  fine  coal  and  cal- 
cined in  three  revolving  cylindrical  furnaces.  These  furnaces  are 
10  meters  long  and  1  meter  in  diameter,  inside,  and  slope  at  an 
angle  of  3°  35'  from  the  horizontal.  They  make  15  revolutions  per 
hour.  The  grate  has  an  area  of  1  square  meter  and  burns  3.1  tons 
of  high-ash  lignite  in  24  hours.  The  ore  remains  in  the  furnace 
about  6  hours.  The  capacity  of  each  furnace  is  16  tons  of  cal- 
cined ore  per  24  hours.  The  results  of  a  year's  operation  of  these 
furnaces  follow: 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     163 


Tons 

Working  hours,  15,800 
Weight  of  raw  material  calcined  

15,137  6  tons 

Weight  of  calcined  product          .        

12  184  8  tons 

Lignite  consumed  

2,296.9  tons 

Cost, 
Francs 

Fuel        

3  25 

Labor                                                              

7376 

Power 

5000 

Oil  and  repairs  

.2651 

Cost  per  ton  of  product                          ..... 

4  7527 

Cost  per  ton  of  raw  material 

3  8250 

New  revolving  furnaces  are  in  course  of  installation  which  will 
be  fitted  with  tubular  boilers,  and  it  is  expected,  through  fuel  econ- 
omy, to  reduce  the  cost  of  calcination  below  francs  3.50  per  ton. 
of  raw  material  treated. 

The  calcined  ore,  after  cooling,  is  delivered  by  a  bucket  elevator 
to  a  series  of  Ferraris  throwing-screens,  making  the  following 
sizes:  through  1  mm.,  1  to  2  mm.,  2  to  3  mm.,  3  to  4  mm.,  4  to 
5  mm.,  and  5  to  6  mm.,  which  sizes  are  treated  separately  by  the 
six  units  comprising  each  magnetic  installation.  In  Plant  No.  2 
the  screen  sizes  run  up  to  10  mm.,  the  oversize  from  which  is 
recrushed;  the  increase  in  size  of  a  certain  proportion  of  the  par- 
ticles is  due  to  swelling  in  the  furnaces.  The  operation  of  the  sep- 
arators is  controlled  by  raising  and  lowering  the  conveyor  belts 
beneath  the  magnets,  this  distance  being  capable  of  adjustment 
between  20  and  40  mm.  The  color  of  the  ore,  as  it  comes  from  the 
furnaces,  is  watched  and  the  distance  between  the  ore  stream  upon 
the  conveyor  belts  and  the  magnets  is  varied  to  suit  the  degree 
of  magnetism  imparted  to  the  ore  by  the  calcination  as  indicated 
by  the  color.  The  combined  capacity  of  the  six  units  is  about  1 
metric  ton  per  hour;  the  separators  require  6  amperes  at  110  volts 
for  excitation,  and  2  E.H.P.  for  operation. 

The  raw  ore  carries  22  per  cent,  zinc,  which  is  increased  to 


164  ELECTRO-MAGNETIC  ORE   SEPARATION 

28  per  cent,  by  the  roast.  Of  the  material  delivered  to  the  mag- 
nets one  third  is  removed  carrying  about  10  per  cent,  zinc,  and  two 
thirds  is  delivered  as  zinc  concentrate  carrying  40  per  cent.  zinc. 
The  zinc  concentrate  carries  a  considerable  amount  of  zincy  dolo- 
mite which  has  been  disintegrated  by  the  calcination,  and  is  jigged 
to  remove  this  waste  and  also  any  fine  coal  remaining  from  the 
furnaces.  The  jigging  of  the  calcined  zincy  dolomite  yields  a  zinc 
oxide  slime  which  assays  from  40  to  48  per  cent  zinc. 

In  1906  this  plant  treated  6,374  tons  of  calcined  material, as- 
saying 25.98  per  cent,  zinc  and  produced  2,264  tons  of  concentrate 
assaying  40.87  per  cent,  zinc,  representing  a  saving  of  66.47  per 
cent,  of  the  zinc.  About  10  per  cent,  of  zinc  is  contained  by  the 
calcined  iron  which  may  not  be  separated  from  it  without  resort 
to  chemical  means. 

To  enrich  still  further  some  of  the  calcined  products  single  sep- 
arators are  employed,  as  is  also  a  high-intensity  separator. 

At  Mercadel,  Santander,  Spain?  there  is  a  magnetic-separation 
plant  treating  oxidized  zinc  ores.  The  ores  carry  calamine  in  a 
gangue  of  limestone  and  limonite,  and  assay  from  12  to  30  per 
cent.  zinc.  The  object  of  the  treatment  is  to  raise  the  zinc  con- 
tent to  50  per  cent.  The  ore  is  rather  clayey  in  character  and  a 
preliminary  treatment  is  necessary  before  calcination.  The  ore  is 
washed,  the  clayey  material  and  the  light  gangue  removed,  and  the 
remainder  from  these  operations  is  calcined.  Ore  above  14  mm.  is 
hand  picked  and  a  considerable  amount  of  limonite  thrown  out; 
all  below  this  size  is  calcined  separately.  The  coarse  (above 
14  mm.)  is  calcined  in  shaft  furnaces,  and  the  finer  material  in 
reverberatories.  The  following  sizes  are  made :  14  to  10  mm.,  10  to 
7J  mm.,  7J  to  4  mm.,  4  to  1}  mm.,  and  through  If  mm. 

The  ore  is  mixed  with  from  1  to  5  per  cent,  of  fine  coal  accord- 
ing to  the  percentage  of  iron  present,  and  calcined  in  reverbatory 
furnaces.  The  calcined  material  carries  from  20  to  40  per  cent, 
zinc  oxide  and  from  20  to  60  per  cent,  magnetic  oxide.  The  pre- 
liminary operations  give  rise  to  fines  which  interfere  with  the  mag- 
netic separation.  After  calcining  the  material  is  run  through  a 
trommel  with  IJ-mm.  holes;  the  coarse  goes  to  a  Herbele-type 
separator  and  the  fines  to  a  deviation  separator. 

The  coarser  sizes,  from  If  mm.  (after  the  fines  are  removed  by 
the  trommel)  are  treated  on  a  trommel  separator  and  two  products 

1  C.  Vial,  "Le  Genie  Civil,"  vol.  xvii,  p.  337. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     165 

are  obtained:  a  clean  zinc  product,  and  a  middling  product  carry- 
ing all  the  iron  and  much  calamine  as  attached  particles.  This  sep- 
arator is  operated  to  remove  all  the  iron  and  make  a  large  mid- 
dling product.  In  treating  this  middling  product  advantage  is 
taken  of  the  extreme  friability  of  the  oxide  of  zinc ;  the  middling 
is  crushed  in  a  Vapert  crusher  so  regulated  that  the  zinc  is  pow- 
dered while  the  magnetic  oxide  of  iron  is  but  slightly  affected. 
The  separator  is  operated  at  15  R.P.M.  and  uses  a  current,  varying 
with  the  sizes  treated,  as  follows: 


Screen  Size,  Millimeters 

Current,  Amperes 

1  1 

to  10                                     

27.85 

10 

to  1\      

26.50 

to  4                     

23.04 

4  t 

o  1? 

21.40 

Mineral  is  treated  carrying  as  much  as  60  per  cent,  magnetic 
oxide  and  as  low  as  22  per  cent,  zinc ;  after  passage  over  the  trom- 
mel separator  the  finished  product  assays  50  per  cent,  zinc  and 
from  8  to  12  per  cent,  oxide  of  iron.  The  iron  tailing  carries  from 
4  to  8  per  cent,  zinc,  mostly  combined  with  the  iron.  With  sizes 
over  14  mm.  hand  picking  was  found  more  efficient  than  the  sep- 
arator, though  it  will  separate  material  as  coarse  as  20  mm.  On 
fines  below  1J  mm.  the  separator  works  poorly.  The  capacity  is 
about  1000  kgm.  per  hour,  and  the  extraction  from  60  to  75  per 
cent,  of  the  contained  iron. 

The  fines  passing  a  IJ-mm.  screen  are  treated  upon  a  deviation 
separator  perfected  by  M.  Vial  and  described  on  another  page  as 
the  Vial  separator.  The  attraction  of  the  stationary  magnets  is 
varied,  according  to  the  material  fed,  by  changing  the  distance 
of  the  magnet  from  the  falling  sheet  of  ore;  the  distance  varies 
from  5  to  25  mm.  The  material  fed  to  the  separator  assays  from 
15  to  35  per  cent,  zinc,  and  carries  from  20  to  40  per  cent,  iron; 
the  concentrate  carries  from  45  to  53  per  cent,  zinc  and  the  tailing 
from  8  to  15  per  cent.  zinc.  The  capacity  is  500  kgm.  per  hour. 
A  certain  amount  of  powder  is  entrained  by  the  iron  which  is 
screened  out  by  a  ^-mm.  screen;  this  powder  assays  from  35  to  40 
per  cent.  zinc.  The  following  typical  results  are  given : 

Rich  feed,  39.87  per  cent,  zinc  and  22.46  per  cent,  iron,  gave  a 


166 


ELECTRO-MAGNETIC   ORE   SEPARATION 


concentrate  with  51.56  per  cent,  zinc  and  10.84  per  cent,  iron, 
removing  200  kgm.  of  waste  per  metric  ton  of  feed.  Lean  feed, 
30.50  per  cent,  zinc  and  31.87  per  cent,  iron,  gave  a  concentrate 
with  48.73  per  cent,  zinc  and  11.80  per  cent,  iron,  removing  350 
kgm.  of  waste  per  metric  ton  of  feed.  The  total  treatment  cost  is 
given  as  4  francs  per  metric  ton,  consisting  of  labor  1.25  francs, 
coal  1.20  francs,  general  expense  and  amortization  1.55  francs. 


PLANTS  SEPARATING  LIMONITE  FROM  OXIDIZED  ZINC 
MINERALS 


PLANT 

Location 

Separator 

Capacity 
Metric 
Tons  per 
10  Hours 

Societa  delle  miniere  de  Montevecchio 
San  B6D6d6tto  Min6S 

Sardinia  .  .  . 
Sardinia  .  .  . 
Sardinia  .  .  . 

Pulaski,Va. 

Humboldt  
Ferraris  No.  2  
Ferraris  No.  2  
l  Wetherill-Rowand 
\  Wetherill  Type  F 

15 

Acquarese  Mines       

Bertha  Mineral  Company 

SEPARATION  OF  HEMATITE 

Hematite,  sp.  gr.  4.5  to  5.3,  is  in  most  occurrences  feebly  mag- 
netic, but  may  be  ferromagnetic.  It  is  separable  raw  in  high- 
intensity  magnetic  fields.  Martite,  of  the  composition  of  hema- 
tite, but  probably  isomorphic  after  magnetite,  is  usually  more 
strongly  magnetic  than  hematite.  Extensive  experiments1  have 
been  carried  out  in  the  roasting  of  hematite  for  magnetism  and  in 
the  separation  of  the  magnetic  oxide  so  formed,  and  also  in  the  di- 
rect separation  of  the  mineral  on  high-intensity  separators.2  That 
these  processes  are  technically  feasible  has  been  amply  proved,  but, 
with  the  present  ruling  prices  for  iron  ores,  the  value  of  the  prod- 
ucts of  magnetic  separation  is  insufficient  to  pay  the  cost  of  pre- 
paring the  ore  for  treatment. 

>Wm.  B.  Phillips,  T.  A.  I.  M.  E.,  October,  1895. 

2  H.  A.  J.  Wilkins  and  H.  B.  C.  Nitze,  T.  A.  I.  M.  E.,  February,  1896. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     167 


SEPARATION  OF  THE  OXIDES  OF  MANGANESE 

Manganite  and  pyrolusite  are  sufficiently  magnetic  to  be  capa- 
ble of  concentration  on  separators  with  high-intensity  fields.  To 
be  commercially  valuable  a  manganese  ore  should  carry  at  least 
40  per  cent,  manganese,  although,  if  accompanied  by  much  iron, 
a  lower  grade  is  suitable  for  spiegel.  The  following  results  are  re- 
ported as  having  been  obtained  on  a  Wetherill  separator  on  culls 
from  a  waste  heap  at  Cave  Springs,  Ga.,  consisting  of  particles  of 
chert  in  a  matrix  of  silicious  pyrolusite  * : 


Per  Cent, 
of  Total 

Per  Cent. 
Manganese 

Per  Cent. 
Quartz 

Feed                         

100 

28.78 

43.00 

Concentrate 

52 

40.91 

20.85 

Tailing                  

48 

15  54 

67  20 

Results  are  reported  2  as  having  been  obtained  on  an  Interna- 
tional separator  showing  the  production  of  a  41.8  per  cent,  man- 
ganese product  from  an  ore  carrying  15  per  cent,  manganese. 


SEPARATION   OF   THE    FRANKLIN   FURNACE    ORES 

At  Franklin  Furnace,  New  Jersey,  the  New  Jersey  Zinc  Co. 
is  operating  a  magnetic-separation  mill  of  1400  tons  daily  capac- 
ity. Three  plants  have  been  erected  by  this  company,  a  description 
of  which  may  be  found  in  Richards's  "  Ore  Dressing,"  pages  1060- 
1065 ;  the  present  mill  was  erected  at  a  cost  of  about  $600,000,  or 
about  $1.75  per  ton  of  annual  capacity.3  The  ore  consists  of 
franklinite,  fowlerite,  tephroite  and  garnet,  magnetic  minerals, 
with  willemite,  zincite,  quartz,  mica,  and  calcite.  The  magnetic 
minerals  are  removed  from  the  mixture  by  twenty-two  Wetherill- 
Rowand  separators,  the  garnet  being  delivered  as  a  separate  prod- 
uct, and  run  to  waste.  This  magnetic  concentrate  is  treated  in 
zinc-oxide  furnaces  and  the  residue,  high  in  manganese,  is  sent  to 

>  H.  A.  J.  Wilkins  and  H.  B.  C.  Nitze,  T.A.I.  M.  E.,  February,  1896. 
2  Jour.  Canadian  Mining  Institute,  F.  T.  Snyder,  March,  1904. 
'"Report  of  the  Zinc  Commission  Appointed  to  Investigate  the  Zinc 
Resources  of  British  Columbia,"  W.  R.  Ingalls,  p.  88. 


168 


ELECTRO-MAGNETIC   ORE   SEPARATION 


spiegel  furnaces.  The  nonmagnetic  product  of  the  separators  is 
jigged  to  separate  the  willemite  and  zincite  from  the  quartz,  calcite 
and  mica,  and  sent  to  the  spelter  furnaces. 

The  preliminary  crushing  of  the  ore  is  done  by  Edison  giant 
rolls  and  is  followed  by  corrugated  and  smooth  rolls.  The  ore 
is  reduced  to  pass  a  No.  10  slot  screen;  the  sizing  is  done  on  Edi- 
son fixed  inclined  screens.  The  ore  is  dried  in  an  Edison  drying 
furnace.  This  consists  of  a  stack  3  ft  square  and  24  ft.  high,  made 
of  cast-iron  plates.  The  interior  is  fitted  with  cast-iron  slats  6  ins. 
wide  and  inclined  at  45°;  these  slats  dip  alternately  to  the  right 
and  to  the  left,  causing  the  ore  to  drop  from  one  to  the  other  and 
exposing  each  particle  to  the  drying  action  of  a  current  of  hot 
gases  from  a  combustion  chamber  outside  the  building.  The  re- 
sults of  the  magnetic  separation  follow: 


Per  Cent, 
of  Feed 

Per  Cent. 
Iron 

Per  Cent, 
Manganese 

Per  Cent. 
Zinc 

Ore 

100  00 

Franklinite  concentrate 

67  48 

29  47 

13  57 

22  94 

Zincite  and  willemite  concentrate 
Tailing  

23.99 
8  53 

2  20 

5.15 

48.96 
A    i  q 

It  is  stated  that   the  cost   of   separation,   exclusive  of   taxes, 
amortization,  and  interest  is  40c.  per  ton  of  ore. 


SEPARATION    OF   WOLFRAMITE 

Wolframite,  sp.  gr.  7.1  to  7.5,  tungstate  of  iron  and  manga- 
nese, is  feebly  magnetic;  specimens  from  some  localities  are  re- 
ported to  be  strongly  magnetic.  Wolframite  frequently  accompa- 
nies cassiterite  in  tin  ores,  and  on  account  of  their  similar  specific 
gravities  (cassiterite  6.4  to  7.02)  these  minerals  may  not  be  sep- 
arated from  each  other  by  specific-gravity  methods.  The  method 
usually  followed  in  treating  crude  ore  or  concentrate  of  this  class 
is  to  convert  any  iron,  or  copper-iron,  sulphides  which  may  be 
present  into  magnetic  compounds  by  roasting,  and  separate  these 
from  the  mixture  by  low-intensity  magnets,  then  to  pass  the  re- 
mainder through  a  stronger  field  which  takes  out  the  wolframite 
as  a  magnetic  product  and  leaves  a  nonmagnetic  tailing  carrying 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     169 

the  tin.  Numerous  tests  on  large  quantities  of  tin-tungsten  con- 
centrates made  preliminary  to  the  installation  of  separation  plants 
have  yielded  high  extractions,  and  a  number  of  these  plants  are  at 
present  in  operation  in  Europe  and  elsewhere.  Most  of  these  in- 
stallations treat  the  product  of  preliminary  water  concentration, 
but  at  least  one  of  them  is  operating  on  raw  ore.  Difficulty  has 
been  experienced  in  the  separation  of  wolframite  from  cassiterite 
through  a  tendency  of  magnetic  particles  to  adhere  to  the  cas- 
siterite, thereby  causing  it  to  be  drawn  into  the  magnetic  product 
when  a  strong  field  is  used  for  separation;  this  tendency  may  be 
overcome  by  treating  the  concentrate  with  sulphuric  acid  and  dry- 
ing before  pasing  it  to  the  separator.  Arsenopyrite  (sp.  gr.  5.67 
to  6.3)  is  of  frequent  occurrence  in  ores  carrying  wolframite: 
upon  roasting  this  mineral  the  arsenic  is  driven  off  and  the  result- 
ing magnetic  oxide  of  iron  separated  from  the  wolframite  by  low- 
intensity  magnets.  Care  must  be  taken  in  the  roasting  of  concen- 
trates carrying  cassiterite  that  the  heat  does  not  rise  to  such  a 
degree  as  to  cause  particles  of  magnetic  oxide  to  become  attached 
to  the  cassiterite  particles,  and  so  cause  them  to  be  drawn  into 
the  wolframite  product. 

At  Ounnislake  Clitters*  England,  tin-tungsten  concentrate  is 
being  separated  on  Humboldt-Wetherill  separators.  The  ore  from 
the  mine  is  crushed  in  breakers  and  rolls,  sized,  and  the  sands  con- 
centrated on  tables  and  the  slimes  with  Luhrig  classifiers.  The 
concentrate  is  roasted  in  a  Bruckner  furnace  having  a  capacity  of 
10  tons  daily;  this  material  carries,  raw,  12  per  cent,  sulphur  and 
arsenic,  principally  the  former,  and  the  iron  with  which  these  ele- 
ments are  combined  is  rendered  strongly  magnetic  in  the  roast. 
The  roasted  concentrate,  after  cooling,  is  fed  to  a  Humboldt-Weth- 
erill separator  which  carries  4  amperes  on  the  first  magnet  and  12 
amperes  on  the  second.  The  first  magnet  removes  the  strongly  mag- 
netic iron  compounds  and  the  second  the  wolframite,  while  the  tin 
is  contained  in  the  nonmagnetic  tailing.  The  tungsten  concentrate 
and  the  tin  product  from  the  separator  are  both  reconcentrated 
to  eliminate  waste.  The  raw  ore  yields  0.378  per  cent,  tin  and  0.72 
per  cent,  tungsten.  The  tungsten  concentrate  carries  from  60 
to  64  per  cent,  tungstate  of  iron,  equal  to  46  to  49  per  cent.  W03. 
The  separator  treats  6  tons  of  concentrate  in  10  hours. 

i  E.  &  M.  J.,  vol.  Ixxvi,  p.  424,  Edward  Skewes. 


170 


ELECTRO-MAGNETIC  ORE  SEPARATION 


FIG.  70. 


At  Redruih?  Cornwall,  England,  the  East  Pool  &  Agar  United 
Mines  Co.  is  operating  a  magnetic-separation  plant  on  concen- 
trates containing  wolframite,  cassiterite,  arsenical  pyrites,  and 
chalcopyrite.  The  ore  is  crushed  by  stamps,  classified,  and  con- 


riG.  71. 


centrated  -on  Wilfley  tables  and  Frne  vanners,  which  deliver  a  con- 
centrate carrying  cassiterite,  wolframite,  and  arsenical  pyrites,  the 

1  E.  &  M.  J.,  vol.  Ixxxiii,  p.  941,  Edward  Walker. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND   MINERALS     171 

gangue  minerals  and  the  ehalcopyrite  being  eliminated  by  the  con- 
centration. These  concentrates  are  roasted  and  the  arsenic  driven 
off,  to  be  recovered  in  the  flues,  while  the  residue  is  again  passed 
over  Wilfley  tables,  yielding  a  product  consisting  of  about  three 
parts  oxide  of  tin  to  one  part  wolframite,  and  carrying  about  5 
per  cent,  magnetic  oxide  of  iron.  After  drying,  this  product  is 
passed  over  a  Humboldt-Wetherill  separator,  which  delivers  three 
products:  magnetic  oxide  taken  out  by  the  first  and  weaker  mag- 
net, wolframite  taken  out  by  the  second  and  stronger  magnet,  and 
a  nonmagnetic  product  carrying  the  tin. 

SEPARATION    OF   MONAZITE    SANDS 

Monazite  sands  are  natural  accumulations  or  concentrations 
which  carry  thorium  and  cerium  oxides  as  their  valuable  constitu- 
ents, together  with  garnet,  menaccanite,  rutile,  zircon,  and  other 
heavy  minerals  as  contaminations.  The  sand  is  usually  concen- 
trated by  washing  and  the  concentrate  separated  on  magnetic  sepa- 
rators. 

Monazite,  sp.  gr.  4.8  to  5.1,  is  feebly  magnetic,  and  is  removed 
from  mixtures  as  a  magnetic  product  in  South  Carolina,  Brazil, 
and  elsewhere.  The  above-mentioned  contaminating  minerals  are 
all  magnetic  in  different  degrees;  menaccanite  the  most  strongly 
magnetic,  followed  by  zircon,  and  rutile  being  the  most  feebly 
magnetic;  garnet  varies  considerably  in  its  magnetic  properties; 
all  are  more  strongly  magnetic  than  monazite,  which  mineral 
is  removed  from  any  nonmagnetic  constituents  of  the  sand  by 
the  last  magnet  encountered  by  the  ore,  which  carries  the  most 
current. 

At  Elleriboro,  South  Carolina,  C.  P.  Meiser  is  operating 
Wetherill-Rowand  separators  on  monazite  sands.  Menaccanite  is 
removed  by  the  first  magnet,  garnet  by  the  second,  and  the  mona- 
zite separated  from  nonmagnetic  impurities  by  the  third. 

At  Sapucaia,  Brazil,  J.  L.  Weiler  is  treating  monazite  sands  on 
a  Humboldt-Wetherill  separator.  The  sands  carry  monazite, 
menaccanite,  wolframite,  cassiterite,  and  quartz.  The  capacity  of 
the  installation  is  2  metric  tons  per  hour. 

At  Rio  de  Janeiro,  Charles  Ban  &  Co.  are  treating  monazite 
sands  on  Humboldt-Wetherill  separators,  the  installation  having 
a  capacity  of  3  metric  tons  per  hour. 


172 


ELECTRO-MAGNETIC  ORE   SEPARATION 


The  following  results  are  reported  from  an  installation  of  the 
Mechernich  separator  in  Brazil  working  on  monazite  sands  car- 
rying cassiterite,  monazite,  and  menaccanite : 


Per  Cent. 
Tin 

Per  Cent. 
ThO3 

Feed     

20  59 

0   78 

Tin  concentrate 

68  30 

0  29 

Thorium  product  

3  32 

1  45 

Menaccanite  tailing     

0  14 

The  tin  recovered  in.  the  tin  concentrate  amounts  to  93.61  per 
cent,  of  the  total  tin  in  the  feed,  and  93.75  per  cent,  of  the  Th02 
is  recovered  in  the  thorium  product. 


SEPARATION  OF  LEUCITE  FROM  LAVA 

In  Italy  there  are  solidified  lava  streams  which  average  20  per 
cent,  leucite,  which  is  valuable  for  its  potassium  content.  Leucite 
is  feebly  magnetic  and  usually  carries  sufficient  iron  as  an  impurity 
to  be  susceptible  to  magnetic  separation. 

The  Societa  Romana  del  solfati  e  chimici,  of  Rome,  is  operating 
two  plants  for  the  recovery  of  leucite  from  lava.  The  leucite  is 
accompanied  by  hornblende,  augite,  and  ferruginous  material, 
which  are  removed  magnetically.  Humboldt-Wetherill  separators 
are  employed  and  the  plants  have  a  capacity  of  90  metric  tons  per 
day.  The  leucite  concentrate  obtained  carries  80  per  cent,  leucite, 
and  is  treated  chemically  for  its  potassium.  This  company  is  op- 
erating a  plant  equipped  with  TJbaldi  separators  producing  a  95 
per  cent,  concentrate  from  lava  containing  25  per  cent,  leucite. 

At  Civita  Castellana,  Italy,  the  Mechernich  separator  is  em- 
ployed for  the  separation  of  leucite.  The  concentrate  obtained  is 
said  to  contain  95  per  cent,  leucite.  The  leucite  here  is  capable  of 
direct  separation. 

CORUNDUM 

Corundum,  sp.  gr.  4.0,  is  feebly  magnetic,  and  may  be  strongly 
magnetic,  through  its  included  magnetite;  emery,  a  variety  of 
corundum,  is  of  a  dark  gray  color,  due  to  magnetite.  Corundum 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     173 

concentrate   is   cleaned   by   magnetic   separation   from   associated 
magnetite. 

HORNBLENDE 

Hornblende,  sp.  gr.  2.9  to  3.4,  is  feebly  magnetic.  It  may  be 
separated  as  a  magnetic  product  by  the  more  intense  separators. 
Occurring  in  a  magnetite  ore,  this  mineral  may  be  responsible  for 
a  loss  of  iron  in  the  tailing,  as  it  carries  iron  but  is  not  sufficiently 
magnetic  to  be  removed  with  the  magnetite  by  the  separators 
usually  employed  on  these  ores. 

CHROMITE 

Chromite,  sp.  gr.  4.32  to  4.6,  is  usually  ferromagnetic;  its  gen- 
eral formula  is  the  same  as  for  magnetite,  with  part  of  the  iron 
replaced  by  chromium;  analysis,  iron  protoxide,  32  per  cent, 
chromium  sesquioxide  68  per  cent. 

DIAMONDS 

At  The  De  Beers  Consolidated  Mines,  Kimberly,  South  Africa, 
the  Humboldt-Wetherill  separator  is  employed  to  remove  magnetic 
minerals  from  concentrate  carrying  diamonds.  This  concentrate 
carries  magnetite,  menaccanite,  chromite,  and  pyrrhotite. 

GALENA 

At  Gem,1  Idaho,  the  Frisco  Mining  Co.  is  employing  three 
Dings  separators  (belt  type)  for  removing  lead  ore  from  zinc  ore 
and  gangue.  The  Jead  is  recovered  as  a  magnetic  product. 

If  a  piece  of  apparently  pure  galena  be  presented  to  the  magnet 
in  the  hand  it  is  attracted  apparently  as  strongly  as  if  it  were  a 
piece  of  iron.  This  phenomenon  may  be  due  to  included  grains 
of  magnetite. 

SEPARATION   OF   BROKEN   HILL    ORES 

At  Broken  Hill,  New  South  Wales,  argentiferous  galena  oc- 
curs with  blende  in  a  gangue  composed  of  quartz,  rhodonite,  and 
garnet.  Upon  concentration  these  ores  yield  a  middling  product 
consisting  of  blende,  rhodonite,  and  garnet,  with  a  little  galena. 

1  Communicated  by  Mr.  W.  R.  Ingalls. 


FIG.   72.  — BROKEN   HILL,   N.  S.  W. 


tiff1 


73.  — BROKEN  HILL,  N.  S.  W. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND   MINERALS     175 

The  re-treatment  of  this  product,  an  immense  quantity  of  which 
has  accumulated  from  past  operations  and  which  is  still  being 
added  to,  is  successfully  accomplished  by  magnetic  separation. 
The  blende  is  feebly  magnetic,  carrying  about  7  per  cent,  iron  and 
2  per  cent,  manganese  in  combination,  and  is  separated  as  a  mag- 
netic product. 

Rhodonite,  sp.  gr.  3.4  to  3.7  (manganese  protoxide,  54.1  per 
cent.;  silica,  45.9  per  cent),  is  feebly  magnetic.  Crane  reports  a 
permeability  of  1.0176  for  a  specimen  from.  Franklin  Furnace, 
N.  J.  It  is  separated  as  a  magnetic  product  at  Franklin  Furnace 
and  at  Broken  Hill. 

Garnet,  sp.  gr.  3.1  to  4.3,  is  in  most  varieties  feebly  magnetic. 
The  permeability  of  this  mineral  depends  upon  its  composition 
and  specimens  of  the  same  variety  from  different  localities  exhibit 
widely  differing  magnetic  qualities.  It  is  separated  as  a  magnetic 
product  at  Broken  Hill  and  at  Franklin  Furnace. 

The  blende  is  more  feebly  magnetic  than  the  rhodonite  and 
garnet,  which  minerals  are  removed  together  as  a  tailing  product. 
The  rhodonite  occasionally  carries  silver,  in  which  case  it  is  sent 
to  the  lead  furnaces  and  smelted  with  the  galena.  The  nonmag- 
netic discharge  from  the  separators,  consisting  of  galena  and 
quartz  with  a  little  feebly  magnetic  blende,  is  concentrated  on 
jigs  and  tables. 

SEPARATION  OF  BROKEN  HILL  TAILING  AT  THE 
PLANTS  OF  THE  SULPHIDE  CORPORATION 

Plant  No.  I.1  This  plant  has  a  capacity  of  150  tons  per  day 
on  tailing  and  middling  carrying  argentiferous  galena  and  blende 
with  rhodonite,  garnet,  and  quartz.  Double-pole  Mechernich  sep- 
arators are  employed  for  the  separation  and  make  three  products : 
garnet  and  rhodonite  tailing,  which  is  sent  underground  and  used 
for  stope  filling ;  magnetic  blende,  a  finished  product ;  nonmagnetic 
residue,  consisting  of  galena  and  quartz  with  a  little  blende,  which 
is  further  treated  on  jigs  and  tables  for  the  production  of  a  lead 
and  a  zinc  concentrate  and  final  tailing. 

The  tailing,  or  middling  from  the  wet  concentration  mills,  is 
loaded  into  trucks  from  the  dumps,  hauled  up  an  incline  and  de- 
livered to  a  belt  conveyor  which  feeds  the  drying  furnace.  This 

1  "Australian  Mining  and  Metallurgy,"  Donald  Clark,  p.  414. 


FIG.   74.  — TAILING  HEAPS,   BROKEN   HILL,   N.  S.   W. 


FIG.  75.  — CONVEYOR  FROM  DUMP,  PLANT  NO.  2,  SULPHIDE  CORPORATION. 


SEPARATION   OF   MISCELLANEOUS  ORES  AND  MINERALS     177 

drying  furnace  consists  of  a  conical  shell  revolving  about  a  hori- 
zontal axis ;  the  material  is  fed  at  the  apex  of  the  cone,  and  is  car- 
ried, by  the  revolution  of  the  shell,  slowly  toward  the  discharge 
end,  where  it  falls  into  a  conveyor  and  is  transported  to  the  trom- 
mels and  screens.  The  dryer  is  heated  by  gases  from  a  fire  box 
located  at  the  feed  end,  the  gases  traversing  the  furnace  in  the 
same  direction  as  the  ore.  The  heat  employed  is  just  sufficient 


FIG.  76.  — DRYING  FURNACE,   PLANT  NO.  2,  SULPHIDE  CORPORATION. 


to  dissipate  the  surface  moisture,  the  sand,  as  it  is  discharged, 
being  just  too  warm  to  hold  in  the  hand. 

The  dried  ore  is  classified  into  three  sizes :  through  -J  mm.,  be- 
tween -J  mm.  and  1  mm.,  and  from  1  mm.  to  3  mm.,  the  oversize  at 
3  mm.  being  recrushed  and  returned  to  the  system.  These  sized 
products  are  treated  separately  on  five  double-pole  Mechernich  sep- 
arators which  yield  two  magnetic  products,  garnet  and  rhodonite, 
and  magnetic  blende,  and  a  nonmagnetic  product  consisting  of 
galena  and  quartz  with  a  little  blende. 

Dust  is  withdrawn  from  each  machine  by  exhaust  fans  and  in 
addition  the  men  are  required  to  wear  respirators  for  protection 
against  the  dust. 


178 


ELECTRO-MAGNETIC  ORE   SEPARATION 
TABLE  OF  RESULTS  ' 


Per  Cent. 
Zinc 

Per  Cent. 
Lead 

Feed                                                       .           .    . 

24  7 

4   01 

Rhodonite  middling  

19.00 

1.80 

Blende  concentrate                 

45  41 

5  .  75 

Nonmagnetic 

5  13 

5  25 

Rhodonite  middling  re-treated  gives 


Per  Cent. 
Zinc 

Per  Cent. 
Lead 

Zinc  concentrate  

38.00 

5.2 

Rhodonite  tailing        ...                       .        ... 

5  50 

Plant  No.  2.2  This  plant  is  equipped  with  Motortype  sepa- 
rators and  has  a  capacity  of  200  tons  per  day  on  the  tailing  product 
of  the  wet-concentration  mills  working  on  ore  from  the  Central 
Mine.  This  material  carries  galena  and  blende  with  quartz  and 
rhodonite,  the  latter  changing  to  rhodochrosite  in  the  lower  levels. 
It  averages,  approximately,  7  ozs.  silver,  5  per  cent,  lead,  and  19  per 
cent.  zinc.  The  various  stages  in  the  treatment  of  this  material 
are: 

(1)  Drying  the  crude  tailing. 

(2)  Preliminary  sizing  and  crushing. 

(3)  Final  classification. 

(4)  Magnetic  separation. 

(5)  Wet  treatment  of  the  nonmagnetic  product. 

The  tailing  is  removed  from  the  dumps  in  the  following  man- 
ner: A  horizontal  belt  conveyor  is  laid  along  the  toe  of  the  dump 
from  which  the  tailing  is  to  be  drawn  off ;  this  conveyor  is  so  con- 
structed as  to  be  free  to  turn  about  a  pivot  at  the  delivery  end  of 

Communicated  by  the  Electromagnetische  Gesellschaft,  Frankfort-a.-M., 
Germany. 

2  Communicated  by  Mr.  James  Hebbard,  manager  of  the  Sulphide  Corpora- 
tion, Broken  Hill,  N.  S.  W. 


FIG.  77.  —  MOTORTYPE  SEPARATOR,  PLANT  NO.  2,  SULPHIDE  CORPORATION. 


FIG.   78.  — SEPARATORS,   PLANT   NO.   2,   SULPHIDE  CORPORATION. 


180  ELECTRO-MAGNETIC  ORE   SEPARATION 

the  belt,  and  the  whole  frame  carrying  the  200  ft.  of  conveyor  is 
free  to  traverse  a  complete  circle  in  azimuth  but  for  the  obstruc- 
tion offered  by  the  dump.  A  hopper  is  mounted  on  rails  on  this 
conveyor  frame  and  can  be  placed  at  any  required  position  along 
the  conveyor.  The  tailing  is  shoveled  from  the  dump  into  this 
hopper.  When  the  dump  has  been  removed  to  a  distance  of  5  ft. 
back  from  the  belt,  along  its  entire  length,  the  framework  is  grad- 


FIG.   79.  — SEPARATION   MILL,   SULPHIDE  CORPORATION. 

ually  moved  in  toward  the  dump,  turning  about  the  pivot  at  the 
delivery  end,  and  shoveling  resumed.  If  necessary,  the  feed  may 
be  maintained  while  the  belt  is  being  moved.  This  movable  hori- 
zontal conveyor  discharges  onto  a  fixed  inclined  conveyor,  which 
in  its  turn  delivers  to  a  revolving  dryer  which  drives  off  the  2  or 
3  per  cent,  moisture  contained  by  the  tailing. 

The  dryer  is  a  revolving  cylinder  4  ft.  in  diameter  and  35  ft. 
long,  set  at  an  angle  of  6J  degrees,  and  having  internal  longitudinal 
ribs  which  serve  to  elevate  and  drop  the  tailing  repeatedly  through 
the  heated  air  as  it  gravitates  toward  the  lower  end  of  the  cylin- 
der. The  tailing  is  fed  from  a  hopper  at  the  upper  end  of  the 
cylinder;  the  fire  box  is  placed  at  the  lower  end  of  the  cylinder 


SEPARATION  OF   MISCELLANEOUS  ORES  AND  MINERALS     181 

into  which  it  discharges  its  gases  through  a  wrought-iron  box  with 
a  sloping  bottom.  The  dried  tailing  falls  from  the  cylinder  into 
this  box  and  is  discharged  from  it  into  a  scraper  conveyor  leading 
to  an  elevator  which  delivers  to  the  trommel.  Here  the;  dried  tail- 
ing is  sized  on  2|-mm.  screens,  the  oversize  being  passed  through 
a  pair  of  30-in.  Cornish  rolls  and  returned  by  the  same  elevator  to 
the  same  trommel.  The  undersize  is  transported  to  the  separation 
mill  by  a  bucket  elevator  which  delivers  to  a  nest  of  four  wind' 
separators.  The  wind  separators  remove  the  finest  particles  (apr 
proximately  from  180  mesh  to  dust)  which  are  sent  to  one 
group  of  separators ;  the  doarser  product  of  the  wind  separators 
is  sent  to  a  series  of  trommels  fitted  with  screens  with  f-mm. 
holes.  The  classification  thus  yields  three  sizes,  coarse,  medium, 
and  fine,  respectively,  from  f  mm.  to  2-J  mm.,  from  f  mm.  to 
180  mesh,  and  from  180  mesh  to  dust.  These  .sized  products 
are  delivered  by  conveyors  to  storage  -bins  which  supply  the 
separators. 

The  separation  is  accomplished  on  Motortype  separators.  The 
relatively  strongly  magnetic  rhodonite  is  separated  directly  as  a 
tailing  product  carrying  little  zinc.  The  feebly  magnetic  blende  is 
removed  as  a  second  product,  and  the  remaining  galena  and  quartz, 
with  a  little  blende,  form  the  nonmagnetic  discharge  from  the 
separators.  The  machines  are  arranged  on  two  floors,  each  floor 
having  a  separate  group  of  magnetic  separators  for  the  treatment 
of  each  of  the  three  sizes  produced  by  the  classification.  The  ma- 
chines on  the  upper  floor  yield  rhodonite  tailing,  zinc  concentrate, 
and  a  galena-quartz  product.  The  machines  on  the  lower  floor  Te- 
treat  the  galena-quartz  product  from  the  primary  machines,  group 
for  group,  and  yield  a  blende  concentrate  which  is  mixed  with  the 
blende  product  from  the  primary  separators,  and  a  final  nonmag- 
netic product  which  is  sent  to  an  auxiliary  wet-concentration 
plant.  The  rhodonite  product  and  the  quartz  tailing  from  the  wet- 
concentration  plant  are  sent  underground  and  there  used  to  fill 
depleted  stopes. 

The  several  products  from  the  separators  are  discharged 
through  rubber  pipes  which  deliver  to  conveyors  running  beneath 
the  machines;  these  conveyors  deliver  their  products  to  the  ship- 
ping bins  alongside  the  railway  track. 

Two  6-ft.  fans  and  several  smaller  auxiliary  fans  are  kept  con- 
tinually at  work  withdrawing  the  dust  from  various  parts  of  the 


182 


ELECTRO-MAGNETIC  ORE   SEPARATION 


SEPARATION  OF   MISCELLANEOUS  ORES  AND  MINERALS     183 

plant.  The  dust  so  collected  is  driven  into  a  wooden  tower,  fitted 
with  suitable  baffles,  where  it  rises  through  a  shower  of  water,  by 
which  it  is  settled  and  carried  to  tanks  from  which  it  is  dis- 
charged periodically. 

All  the  machinery  in  the  plant  is  operated  by  individual  motors 
which  receive  their  current  from  a  central  power  station. 

In  1906  this  plant  treated  47,326  tons  of  tailing  assaying  6 
ozs.  silver,  5.2  per  cent,  lead,  21.8  per  cent,  zinc,  and  recovered  17,- 
753  tons  of  zinc  concentrate  assaying  39.6  per  cent,  zinc,  a  sav- 
ing of  68.1  per  cent. 

SEPARATION  AT  THE  WORKS  OF  THE  AUSTRALIAN  METAL 
COMPANY,  BROKEN  HILL,  N.  S.  W.1 

The  material  treated  is  tailing  from  water  concentration,  car- 
rying galena  and  blende  with  rhodonite,  garnet,  and  quartz.  First 
the  garnet  and  rhodonite  are  removed  as  a  magnetic  product,  and 
finally  the  blende,  leaving  the  galena  with  the  quartz  as  a  nonmag- 
netic product,  from  which  the  galena  is  finally  removed  by  water 
concentration.  About  130,000  tons  had  already  been  treated  at 
the  time  of  writing. 

The  tailing  from  the  piles  is  trucked  to  a  hopper  which  delivers 
an  even  feed  onto  a  Eobins  belt  conveyor,  elevated  and  passed  into 
a  revolving  dryer  running  on  friction  rolls.  The  heat  is  just  suffi- 
cient to  dissipate  the  moisture,  which  amounts  to  from  2  to  3  per 
cent. 

From  the  dryers  the  tailing  passes  to  a  shaking  screen,  a  hood 
being  placed  above  the  screen  to  draw  off  any  dust.  The  material 
which  does  not  pass  through  the  coarse  screen  (9  mesh),  which  is 
only  about  2  per  cent,  of  the  total,  passes  to  rolls  for  crushing. 
The  screened  material  goes  to  the  boot  of  an  elevator  and  is  car- 
ried to  the  top  of  the  building.  It  is  then  distributed  between  two 
double  trommels,  with  screens  giving  three  products — 2,  3,  and  4 
— No.  1  being  reduced. 

No.  1  retained  on- a  sieve  having  9  holes  per  linear  inch. 
No.  2  passes  No.  1  but  is  retained  on  a  20-mesh  screen. 
No.  3  passes  No.  2  but  is  retained  on  a  40-mesh  screen. 
No.  4  passes  through  the  40-mesh  screen. 

1  "Australian  Mining  and  Metallurgy,"  Donald  Clark,  p.  415. 


184 


ELECTRO-MAGNETIC  ORE   SEPARATION 


The  last  product  contains  everything  below  40  mesh  except 
dust,  which  is  drawn  away  through  steeply  sloping  pipes  connected 
with  a  fan,  and  sent  to  a  dust  chamber.  The  fines  are  treated  by 
four  Ullrich  separators  and  the  coarse  by  four  machines  of  the 
same  type.  Each  machine  contains  four  separating  armatures  set 


<FIG.  81.  — PLAN  AND  SECTION  OF  THE  SEPARATION  PLANT.  AUSTRALIAN 

METAL  CO. 

above  and  below  in  pairs.  The  ore  is  fed  in  a  steady  stream 
through  a  hopper  having  a  distributing  arrangement  consisting  of 
inclined  shaker-plates,  and  falls  on  the  upper  armatures.  The  cur- 
rent is -so  adjusted  on  the  upper  armatures  that  only  garnet  and 
rhodonite  adhere  and  are  removed.  The  balance  of  the  ore  drops 
on  to  the  lower  armatures  and  a  stronger  current  here  removes  the 
blende,  practically  clean. 


SEPARATION  OF   MISCELLANEOUS  ORES  AND  MINERALS     185 

The  final  products  from  the  separators  are  garnet  and  rho- 
donite from  the  upper  armatures,  and  blende  from  the  lower;  the 
nonmagnetic  material  escaping  the  attraction  of  the  magnets  con- 
sists mainly  of  quartz  and  galena,  with  a  little  blende.  There  are 
eight  Ullrich  separators  on  the  top  floor,  four  treating  coarse  sizes 
and  four  working  on  fines.  The  blende  remaining  with  the  ga- 
lena and  quartz  is  removed  on  two  half-machines  placed  on  a 
lower  floor;  the  tailing  from  these  machines  consists  almost  en- 
tirely of  galena  and  quartz;  this  goes  to  an  ordinary  wet-dressing 
plant,  the  coarse  being  concentrated  on  jigs  and  the  fines  on  Wil- 
fley  tables. 

At  present  about  200  tons  of  tailing  are  being  treated  per  day, 
and  about  100  tons  of  zinc  concentrates  are  recovered;  from  50 
to  60  tons  of  lead  concentrate  are  recovered  per  fortnight. 

From  75  to  80  H.P.  are  required  to  operate  the  plant.  Each 
machine  requires  about  1£  M.  and  E.H.P.  The  current  indicators 
show  120  amperes  at  110  volts.  Steam  is  generated  in  two  mul- 
titubular  boilers  at  120  Ibs.  per  square  inch  and  utilized  in  a  com- 
pound engine;  the  power  installation  is  about  double  the  present 
requirements. 

The  zinc  concentrate  from  the  fines  assays  46  per  cent.  Zn. 
The  zinc  concentrate  from  the  medium  assays  43  per  cent.  Zn. 
The  zinc  concentrate  from  the  coarse  assays  41  per  cent.  Zn. 

The  recovery  of  zinc  by  the  first  machines  is  from  82  to  86 
per  cent. 

The  lead  concentrate  from  the  fines  assays  45  to  47  per  cent. 

The  lead  concentrate  from  the  medium  assays  42.5  to  48.6  per  cent. 

The  lead  concentrate  from  the  coarse  assays  40  to  42  per  cent. 

The  recovery  of  lead  is  80  per  cent.  The  lead  concentrates 
are  rich  in  silver;  the  zinc  concentrates  run  from  15  to  18  ozs. 
per  ton. 

Ten  men  are  required  per  shift  to  run  the  plant.  The  dust 
problem  is  a  serious  one,  but  an  effort  has  been  made  to  mini- 
mize the  evil  by  the  use  of  exhaust  pipes  with  powerful  fans  con- 
nected with  every  appliance.  The  dust  is  finally  collected  in  a 
chamber,  is  wetted  down,  and  sold  as  slime.  It  amounts  to  about 
2J  per  cent,  of  the  material  treated. 


186  ELECTRO-MAGNETIC  ORE   SEPARATION 


SEPARATION  AT  THE  JUNCTION  NORTH  MINE  1 

The  ore  treated  carries  argentiferous  galena  and  blende  in  a 
gangue  of  rhodonite  and  garnet  sandstone;  it  assays  12.6  ozs.  sil- 
ver, 17.9  per  cent,  lead,  and  9.1  per  cent.  zinc.  Ullrich  separators 
are  employed. 

The  ore  is  crushed  in  rock  breakers,  from  which  it  is  carried 
on  a  shaking  conveyor  to  a  revolving  dryer,  and  thence  to  a  bin. 
It  is  next  crushed  in  a  ball  mill  to  1  mm.  and  sent  to  trommels; 
here  the  ore  is  classed  into  the  following  sizes :  between  1  mm.  and 
50  mesh,  between  50  and  25  mesh,  and  through  50  mesh.  The 
first  two  sizes  are  fed  separately  to  the  separators  while  the  fines 
through  50  mesh  are  treated  on  Wilfley  tables  and  vanners. 

The  separators  make  the  following  products :  ( 1 )  Low  grade 
tailing,  sent  below  for  use  as  stope  filling,  consisting  of  rhodonite 
and  garnet;  (2)  a  middling  product  which  is  further  separated 
into  (a)  zincy  high-grade  lead,  and  (b)  zinc  concentrates;  (3) 
lead  concentrate. 

Dust  is  collected  by  centrifugal  fans  and  after  wetting  down 
treated  on  vanners. 

»  E.  &  M.  /.,  vol.  Ixxx,  p.  385. 


INDEX 


Adjustments  of  separators,  16. 
Agustin,  M.  G.,  113. 
Ain  Barbar,  Algeria,  154. 
Air  gap,  11. 

liquid,  4. 

permeability  of,  3. 
Apatite,  80,  82. 
dust,  15. 

Arsenopyrite,  169. 
Attraction,  magnetic,  3,  11. 
Augite,  172. 
Austinville,  Va.,  160. 

Balia  Karaidin,  Turkey,  137. 
Ball  Mills,  Grondal,  105,  111. 
Ball-Norton  belt  separator,  16,  22,  89,  92,  95;  96. 
cobbing  separator,  40,  86,  88. 
double-drum  separator,  24,  93,  95,  102,  105. 
Beach  sands,  83. 
Beckert,  T.,  101. 
Bennie,  P.  McN.,  86. 
Benson  Mines,  N.  Y.,  96. 
Bendisberg,  Germany,  146. 
Bensberg,  Germany,  146. 
Bilboa,  Spain,  146. 

Blake-Morscher  Electrostatic  Separators,  135. 
Blende,  116. 

effect  of  heat  on,  117. 

magnetic,  10,  120. 
Bliesenbach,  Germany,  146. 
Bredsjo,  Sweden,  81,  108. 

Briquetting  magnetite  concentrate,  84,  85,  98,  101. 
Broken  Hill,  N.  S.  W.,  7,  159,  173,  183. 
Bromide  of  copper,  5. 
Budel,  Spain,  146. 

Calamine,  159. 

Calcination  of  siderite,  138,  139. 

187 


188  INDEX 

Canon  City,  Colo.,  136. 

Capacity  of  magnetic  separators,  16. 

Carlshof,  Germany,  134. 

Cassiterite,  168,  169,  170,  172. 

Caucasia,  Russia,  156. 

Chalcopyrite,  6,  153,  154,  156,  157. 

Chateaugay,  N.  Y.,  91. 

Chromite,  4,  173. 

Civita  Castellana,  Italy,  172. 

Clarke,  Donald,  175,  183. 

Cleveland-Knowles  Separator,  46,  124,  127,  12,8,  129,  131,  171. 

Cobbing,  magnetic,  80. 

separators,  41,  42,  43. 
Concentration,  magnetic,  5. 
Cooling  ores  after  roasting,  21,  125,  127. 
Copper  carbonate,  157. 
Cost  of  magnetic  separation,  17. 
Crane,  Prof.,  138,  158,  159. 
Cordova,  Spain,  156. 
Corinth,  Vt.,  153. 
Crushing  ores,  18. 
Cumberland,  R.  I.,  83. 
Cupriferous  pyrites,  153. 

Dannemora,  Sweden,  103. 
Dellvik-Grondal  separators, -25,  105,  107,  108. 
Denver,  Colo.,  121,  135. 
Diamagnetics,  3.       - 

Dings  separator,  17,  44,  122,  123,  130,  131,  132,  173. 
Dortmund,  Germany,  156. 
Dry  crushing,  14,  19. 
Drying  ores,  20,  87,  143,  145, 168, 177, 180. 
Dust,  elimination  of,  181. 
magnetic,  15. 

Edison,  N.  J.,  84,  98. 
Edison  belt  separator,  40. 

separator,  14,  38,  100. 
Ellenboro,  S.  C.,  171. 
Ems,  Germany,  16,  144. 
Entrainment,  9,  14. 
Ericksson  Separator,  35, 103)  113.         «  =    .-.,.. 

Feed,  depth  of,  9. 
Feeding  devices,  15. 
Ferraris,  E.,  160. 

crossbelt  separator,  54,  162,  166. 

drum  separator,  56. 


INDEX  189 


Ferromagnetic  minerals,  4. 

Field,  behavior  of  substances  in  magnetic,  3. 

intensity  of  magnetic,  11. 

of  magnetic  separation,  5. 

production  of  a  dense,  11. 
Fines,  separation  of ,  14. 
Floberget,  Sweden,  105. 
Forsgren  separator,  36,  103,  105. 
Fowlerite,  167. 

Franklin  Furnace,  N.  J.,  7,  167. 
Franklinite,  4,  167. 
Fredricktown,  Mo.,  154. 
Friedrichssegen,  Germany,  146. 
Froeding  separator,  34. 
Furnaces,  roasting,  121,  123,  124,  127,  128,  129,  132,  154. 

Galena,  effect  of  heat  on,  121. 

magnetic,  5,  173. 

roasting  furnace,  124,  127,  128,  129. 
Garnet,  156,  157,  167,  171,  173,  175. 
Gem,  Idaho,  5,  173. 
Genumari,  Italy,  146. 
Granberry,  J.  H.,  86. 
Grangesberg,  Sweden,  103. 
Gregory,  F.  W.,  123. 
Gromier,  M.  G.,  150. 
Grondal  ball  mills,  105,  111. 

cobbing  separator,  43. 

slime  separator,  32,  97. 

Type  I  Separator  (see  Dellvik-Grondal  Separator). 

Type  II  Separator,  27,  105,  107. 

Type  III  Separator,  28,  97. 

Type  IV  Separator,  28. 

Type  V  Separator,  30,  96,  97, 101. 
Guldsmedsyttan,  Sweden,  101. 
Gunnislake  Glitters,  England,  169. 

Hamborn,  Germany,  134. 

Hansel,  N.  V.,  91. 

Hazel  Green,  Wis.,  127. 

Hebbard,  James,  178. 

Hematite,  7,  166. 

Herbele  dry  separator,  57,  150,  158,  164. 

wet  separator,  52,  102,  134. 
Herrang,  Sweden,  19,  81,  96. 
Hibernia,  N.  J.,  81,  95. 
Hoffman,  H.  O.,  117. 


190  INDEX 

Hornblende,  172,  173. 
Huanchaca,  Bolivia,  132. 
Humboldt,  ring  separator  58. 

single  roller  separator,  53,  134. 

wet  separator,  51. 

Wetherill  Separator,  16,  63, 134,  137,  141,  144,  145, 146, 155, 156, 
166,  169,  170,  172. 

Wetherill  tandem  separator,  46. 
Hunter,  H.  G.,  153. 

Ilmenite,  4,  83,  171. 
Ille  et  Vilaine,  France,  137. 
Induction,  magnetic,  3,  10. 
Ingalls,  W.  R.,  138,  149,  167,  173. 
Innsbruck,  Austria,  156. 
International  separator,  70,  135. 
Iron  ores,  separation  of  lean,  7. 

Joplin,  Mo.,  132. 

Kaslo,  B.  C.,  132. 
Kattowitz,  Germany,  134. 
Keating,  J.  B.,  156. 
Kimberley,  South  Africa,  173. 
Klacka,  Sweden,  105. 
Knowles  Separator,  59. 
Kokomo,  Colo.,  120. 
Korda,  D.,  58,  150,  154,  155,  157. 
Krompach,  Austria,  151. 

Langguth,  E.,  5,  10,  101. 

Lauenberg,  Germany,  145. 

Leadville,  Colo.,  119,  135. 

Lebanon,  Pa.,  96. 

Leucite,  172. 

Leuschner  table  separator,  51. 

Limonite,  7,  159. 

calcination  of,  159,  162,  164. 
Lipine,  Germany,  134. 
Littlefeld,  Germany,  146. 
Long  Island,  N.  Y.,  magnetic  sands,  83. 
Lulea,  Sweden,  82. 
Lyon  Mountain,  N.  Y.,  81,  91. 

Magnetic  attraction,  3,  11. 

cobbing,  80. 

induction,  3,  10. 

Magnetic  ores,  briquetting  of,  84,  85,  98,  101. 
Magnetic  sands,  84. 


INDEX  191 


Magnetic  separation,  3. 

as  a  process,  7. 

cost  of,  7. 

principles  of,  9. 
Magnetic  separators,  capacity  of,  16. 

classification  of,  22. 

cost  of,  17. 

requirements  of,  16. 
Magnetism,  residual,  13. 
Magnetite  4,  10,  79. 
Maiern,  Austria,  149. 
Manganese,  oxides  of,  167. 
Marcosite,  116. 

roasting  of,  116. 
Marienhuette,  Germany,  146. 
Marmetite,  116,  120. 
Martite,  166. 
McClave,  J.  M.,  123. 
McNeill,  H.  C.,  158. 

Mechernich  separator,  64,  134,  145,  146,  155,  172,  175,  177. 
Meiser,  C.  P.,  171. 
Menaccanite,  4,  83,  171. 
Mercadel,  Spain,  160,  164. 
Meusen,  Germany,  145. 
Middling  product,  necessity  of,  13. 
Mineral  Point,  Wis.,  129. 
Mineville,  N.  Y.,  81,  82,  86. 
Minaca,  Chihuahua,  Mexico,  137. 
Moisie,  Quebec,  83. 

Monarch  separator,  24,  93,  95,  102,  105. 
Monazite  sands,  171. 
Monteponi,  Sardinia,  160. 
Motortype  separator,  65,  178,  181,  185. 
Mount  Hope,  N.  J.,  96. 
Munsterbusch,  Germany,  134. 

Neunkirchen,  Germany,  140,  146. 
Newland,  D.  H.,  91. 
Nitze,  H.  B.  C.,  166,  167. 
Norton,  D.  H.,  91. 

Odling  separator,  53,  159. 
Oxygen,  paramagnetism  of,  4. 

Paramagnetics,  3,  4. 

Payne  separator,  69. 

Permeability,  methods  of  determining,  4. 

specific  magnetic,  4. 

unit  of,  3. 


192  INDEX 

Pentlandite,  158. 

Persberg,  Sweden,  107. 

Petersson,  Prof.,  98,  103,  104,  105. 

Peyrebrune,  Germany,  134. 

Phillips,  W.  B.,  166. 

Pitkaranta,  Finland,  19,  81,  85. 

Platteville,  Wis.,  128. 

Pola  de  Lena,  Spain,  156. 

Polarity,  induction  of,  3. 

Port  Henry,  N.  Y.,  96. 

Port  Orem,  N.  J.,  81,  95. 

Preparation  of  the  ore  for  treatment,  18. 

Presentation  of  ore  to  magnets,  9,  10,  12. 

Primosigh  dry  separator,  67,  151. 

wet  separator,  50. 
Pueblo,  Colo.,  134. 
Pulaski,  Va.,  166. 
Pyrite,  115. 

cost  of  roasting,  17. 

cupriferous,  153. 

diamagnetism  of,  5. 

elimination  of,  83. 

roasting  for  magnetism,  116. 
Pyrrhotite,  4,  157,  158. 

elimination  of,  83,  173. 

Raglan,  Ont.,  114. 
Ravalo,  Sweden,  134. 
Removal  of  attracted  particles,  12. 
Repulsion,  magnetic,  3. 
Rhodonite,  10,  173,  175. 
Richards,  R.  H.,  98,  119,  150,  167. 
Rio  de  Janeiro,  Brazil,  171. 
Roasting,  cost  of,  17. 

furnaces,  Galena,  124,  127,  128. 

McDougal,  154. 

White  Howell,  132. 

Wilfley,  121,  123,  129. 
Rome,  Italy,  172. 

Romne,  Sweden,  107. 

Rutile,  171. 

Ryllshytans,  Sweden,  114. 

Sahlin,  A.,  83. 
San  Pedro,  N.  M.,  157. 
Santa  Eulalia,  Spain,  113. 
Sapucaia,  Brazil,  171. 
Sardinia,  160,  166. 
Saxburget,  Sweden,  158. 


INDEX  193 

Separation,  preliminary,  21. 
Siderite,  138. 

calcining,  139,  150. 

cost  of  calcining,  17. 

concentration  of,  5,  150,  151. 

separation  raw,  140. 
Sizing,  necessity  of,  7,  20. 
Skewes,  Edward,  169. 
Smithsonite,  159. 
Snyder,  F.  T.,  167. 
Solsbury,  N.  Y.,  96. 
Sphalerite,  116. 

Stern  type  separator,  48,  132,  134. 
Stockholm,  Sweden,  156. 
Strassa,  Sweden,  81,  108. 
Sudbury,  Ont.,  158. 
Sulphur,  diamagnetism  of,  4. 

elimination  of,  83. 
Svarto,  Sweden,  81,  82. 
Switzer,  F.  R.,  96. 

Temperature,  effect  of,  on  magnetic  attraction,  5. 
Tephroite,  167. 
Testing  ores,  17. 
Torrelavega,  Spain,  134. 

Ubaldi  separator,  72,  172. 

Ullrich  separator,  185. 

Unter  Eschbach,  Germany,  146. 

Vial,  M.  C.,  164. 

separator,  57. 

Walker,  Edward,  170. 

Weiler,  J.  L.,  171. 

Weiskopf,  Dr.,  107,  108,  119. 

Wenstrom  cobbing  separator,  43,  105,  106. 

separator,  41,  103. 

Wetherill-Rowand  separator,  61,  89,  135,  137,  153,  157,  166,  167. 
Wetherill  horizontal  separator,  75. 

inclined  separator,  76. 

Type  F  separator,  33,  89,  136,  166. 
Wilfley  roasting  furnace,  121,  123. 
Wilkins,  H.  A.  J.,  166,  167. 
Wolframite,  168. 

Yerington,  Nev.,  156. 

Zinc  ores,  separation  of,  6. 
Zircon,  171. 


RETURN     ENGINEERING  LIBRARY 
TO—*  642-3366 


LOAN  PERIOD  1 

2 

3 

4 

5 

6 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 
Overdues  subject  to   replacement  charges 

DUE  AS  STAMPED  BELOW 


MAR  1Q19<% 


FORM  NO.  DD11 


UNIVERSITY  OF  CALIFORNIA,  BERKELEY 

BERKELEY,  CA  94720 

®$ 


33874 


U.C.  BERKELEY  LIBRARIES 


€035(3^5478 


193292 


